Indirect effects of fidelity to the family check-up on changes in parenting and early childhood problem behaviors

OBJECTIVE

This study examines observations of client in-session engagement and fidelity of implementation to the Family Check-Up (FCU) as they relate to improvements in caregivers' positive behavior support (PBS) and children's problem behavior in the context of a randomized prevention trial. The psychometric properties of fidelity scores obtained with a new rating system are also explored.

METHOD

The FCU feedback sessions of 79 families with children with elevated problem behavior scores at age 2 were coded by trained raters of fidelity, who used an observational coding system developed specifically for this intervention model.

RESULTS

Path analysis indicated that fidelity to the FCU results in greater caregiver engagement in the feedback session, which directly predicts improvements in caregivers' PBS 1 year later (β = 0.06, 95% CI [.007, .129]). Similarly, engagement and PBS directly predict reductions in children's problem behavior measured 2 years later (β = -0.24, 95% CI [-.664, -.019]).

CONCLUSIONS

These results suggest fidelity within the context of this randomized intervention trial. Ratings of fidelity to the FCU covary with observed improvements in parenting and children's problem behavior in early childhood. Overall reliability of the fidelity scores was found to be acceptable, but some single-item reliability estimates were low, suggesting revisions to the rating system might be needed. Accurately assessing fidelity and understanding its relationship to change during intervention studies is an underdeveloped area of research and has revealed some inconsistent findings. Our results shed light on the mixed conclusions of previous studies, suggesting that future research ought to assess the role of intervening variable effects, such as observed engagement.

Temperature effects on the fidelity of a thermostable HIV-1 reverse transcriptase

Transcriptomics and gene expression analysis are largely dependent of the availability of efficient thermostable reverse transcriptases (RTs). However, the intrinsic fidelity of DNA synthesis catalyzed by retroviral RTs is low. Reported error rates are in the range 1.2 × 10(-5)-6.7 × 10(-4), with oncoretroviral RTs being the most faithful enzymes. Wild-type HIV-1 group O (HIV-1O) RT is a thermostable polymerase that is able to synthesize cDNA at temperatures as high as 70 °C. At 37 °C, its error rate has been estimated at 5.8 × 10(-5) in M13mp2 lacZ-based forward mutation assays. However, at higher temperatures (e.g. 50 and 55 °C), the accuracy of HIV-1O RT is increased by approximately two- to five-fold. At 55 °C, the HIV-1O RT error rate (1.3 × 10(-5)) was similar to that shown by the AffinityScript (Agilent Technologies Inc., La Jolla, CA, USA) RT, a commercially available thermostable murine leukaemia virus RT. At higher temperatures, the increased accuracy of the HIV-1 enzyme results from a lower base substitution error rate, although it shows a higher tendency to introduce frameshifts. Kinetic studies carried out with model template-primers suggest minor differences in nucleotide discrimination, although, at higher temperatures, HIV-1O RT showed a reduced ability to extend mispaired template-primers.

Implementation of a culturally tailored diabetes intervention with community health workers in American Samoa

PURPOSE

The purpose of this article is to answer key implementation questions from our translation research with a primary care-based, nurse-community health worker (CHW) team intervention to support type 2 diabetes self-management.

METHODS

Descriptive data are given on intervention delivery, CHW visit content, patient safety, and intervention costs, along with statistical analyses to examine participant characteristics of higher attendance at visits.

RESULTS

In the intervention sample (n = 104), 74% (SD = 16%) of planned intervention visits occurred, guided by an algorithm-based protocol. Higher risk participants had a significantly lower dose of their weekly assigned visits (66%) than those at moderate (74%) and lower risk (90%). Twenty-eight percent of participants moved to a lower risk group over the year. Estimated intervention cost was $656 per person. Participants with less education were more likely to attend optimal percentage of visits.

CONCLUSIONS

A nurse-CHW team can deliver a culturally adapted diabetes self-management support intervention with excellent fidelity to the algorithm-based protocols. The team accommodated participants' needs by meeting them whenever and wherever they could. This study provides an example of adaptation of an evidence-based model to the Samoan cultural context and its resource-poor setting.

Survivor experience of a child sexual abuse prevention program: a pilot study

Addressing gaps in the research, the current study assesses the impact of a community-based child sexual abuse prevention program on known survivor knowledge/skills, disclosures, and subjective experience. Methodologically, novel measures of program fidelity and implementation cost are applied. A pre- posttest wait-list control design was utilized with intervention (n = 10) and comparison groups (n = 10). Measures included a standardized knowledge/skill questionnaire, coding of disclosures, subjective experience questionnaires, in-depth interviews, video analysis of program adherence, and a measure of cost. Analysis involved nonparametric tests and thematic analysis of interview and video data. Cost was calculated for the group and per survivor. Survivors achieved significant gains in knowledge/skills, made further disclosures, and were positive about their program experience. No gains were identified in the control group. Costs were small. Future studies need to explore survivor experience of programs delivered in classrooms.

The reporting of fidelity measures in primary prevention programmes for eating disorders in schools

OBJECTIVE

The aim of this paper was to examine the extent to which controlled trials of face-to-face school-based primary prevention for eating disorders report their strategies for maintaining fidelity.

METHOD

A systematic review located 38 articles eligible for inclusion. These studies were assessed using 18 criteria for reporting fidelity maintenance strategies based on those recommended by the Treatment Fidelity Workgroup of the National Institute of Health Behavior Change Consortium.

RESULTS

Fidelity reporting was generally poor. The studies reported between 22% and 56% of fidelity criteria. Detailed reporting of curriculum-as-usual control conditions was generally lacking, as were methods to ensure high-quality training and mechanisms to assess provider adherence to intervention protocol.

DISCUSSION

Poor fidelity assessment and reporting is a problem in school-based primary prevention programmes for eating disorders. Recommendations for improving fidelity maintenance and reporting practices are provided.

Translocation and fidelity of Escherichia coli RNA polymerase

Exonuclease (exo) III was used as a probe of the Escherichia coli RNA polymerase (RNAP) ternary elongation complex (TEC) downstream border. In the absence of NTPs, RNAP appears to stall primarily in a post-translocated state and to return slowly to a pre-translocated state. Exo III mapping, therefore, appears inconsistent with an unrestrained thermal ratchet model for translocation, in which RNAP freely and rapidly oscillates between pre- and post-translocated positions. The forward translocation state is made more stable by lowering the pH and/or by elevating the salt concentration, indicating a probable role of protonated histidine(s) in regulating accurate NTP loading and translocation. Because the post-translocated TEC can be strongly stabilized by NTP addition, NTP analogs were ranked for their ability to preserve the post-translocation state, giving insight into RNAP fidelity. Effects of NTPs (and analogs) and analysis of chemically modified RNA 3′ ends demonstrate that patterns of exo III mapping arise from intrinsic and subtle alterations at the RNAP active site, far from the site of exo III action.

Splicing fidelity: DEAD/H-box ATPases as molecular clocks

The spliceosome discriminates against suboptimal substrates, both during assembly and catalysis, thereby enhancing specificity during pre-mRNA splicing. Central to such fidelity mechanisms are a conserved subset of the DEAD- and DEAH-box ATPases, which belong to a superfamily of proteins that mediate RNP rearrangements in almost all RNA-dependent processes in the cell. Through an investigation of the mechanisms contributing to the specificity of 5' splice site cleavage, two related reports, one from our lab and the other from the Cheng lab, have provided insights into fidelity mechanisms utilized by the spliceosome. In our work, we found evidence for a kinetic proofreading mechanism in splicing in which the DEAH-box ATPase Prp16 discriminates against substrates undergoing slow 5' splice site cleavage. Additionally, our study revealed that discriminated substrates are discarded through a general spliceosome disassembly pathway, mediated by another DEAH-box ATPase Prp43. In their work, Tseng et al. described the underlying molecular events through which Prp16 discriminates against a splicing substrate during 5' splice site cleavage. Here, we present a synthesis of these two studies and, additionally, provide the first biochemical evidence for discrimination of a suboptimal splicing substrate just prior to 5' splice site cleavage. Together, these findings support a general mechanism for a ubiquitous superfamily of ATPases in enhancing specificity during RNA-dependent processes in the cell.

Evaluating fidelity to the wraparound service model for youth: application of item response theory to the Wraparound Fidelity Index

The wraparound process is a mechanism for multisystem planning and care coordination for youth with serious emotional and behavioral problems. Fidelity monitoring is critical to effective implementation of evidence-based practices in children's mental health, as it helps ensure that complex interventions like wraparound are implemented as intended. The 40-item Wraparound Fidelity Index, Version 4 (WFI-4; Bruns, Burchard, Suter, Leverentz-Brady, & Force, 2004) is the most frequently used measure of fidelity to the wraparound process, but analysis of its psychometric properties is insufficient. An item response theory approach, Rasch partial credit models for ordered polytomous data, was used on ratings from 1,234 facilitators, 1,006 caregivers, and 221 team members, focused on 1,478 youths (55% male). Results indicated the WFI-4 measured a unidimensional construct, with little evidence of item bias and good item and model fit. However, the item information curve was skewed, with most people endorsing high-fidelity responses, and several items had duplicative location estimates. A reduced 20-item measure is proposed. Internal reliability estimates for scores from this reduced measure were approximately equivalent to the longer measure. However, both versions would benefit from additional items located in the highest fidelity area of either version of the scale where scores by greater than half of our sample fall, but only 3 items are located.

Sustainability of knowledge translation interventions in healthcare decision-making: protocol for a scoping review

INTRODUCTION

Knowledge translation (KT also known as research utilisation, translational medicine and implementation science) is a dynamic and iterative process that includes the synthesis, dissemination, exchange and ethically sound application of knowledge to improve health. After the implementation of KT interventions, their impact on relevant outcomes should be monitored. The objectives of this scoping review are to: (1) conduct a systematic search of the literature to identify the impact on healthcare outcomes beyond 1 year, or beyond the termination of funding of the initiative of KT interventions targeting chronic disease management for end-users including patients, clinicians, public health officials, health services managers and policy-makers; (2) identify factors that influence sustainability of effective KT interventions; (3) identify how sustained change from KT interventions should be measured; and (4) develop a framework for assessing sustainability of KT interventions.

METHODS AND ANALYSIS

Comprehensive searches of relevant electronic databases (eg, MEDLINE, EMBASE, Cochrane Central Register of Controlled Trials), websites of funding agencies and websites of healthcare provider organisations will be conducted to identify relevant material. We will include experimental, quasi-experimental and observational studies providing information on the sustainability of KT interventions targeting chronic disease management in adults and focusing on end-users including patients, clinicians, public health officials, health services managers and policy-makers. Two reviewers will pilot-test the screening criteria and data abstraction form. They will then screen all citations, full articles and abstract data in duplicate independently. The results of the scoping review will be synthesised descriptively and used to develop a framework to assess the sustainability of KT interventions.

DISCUSSION AND DISSEMINATION

Our results will help inform end-users (ie, patients, clinicians, public health officials, health services managers and policy-makers) regarding the sustainability of KT interventions. Our dissemination plan includes publications, presentations, website posting and a stakeholder meeting.

The role of treatment fidelity on outcomes during a randomized field trial of an autism intervention

This randomized field trial comparing Strategies for Teaching based on Autism Research and Structured Teaching enrolled educators in 33 kindergarten-through-second-grade autism support classrooms and 119 students, aged 5-8 years in the School District of Philadelphia. Students were assessed at the beginning and end of the academic year using the Differential Ability Scales. Program fidelity was measured through video coding and use of a checklist. Outcomes were assessed using linear regression with random effects for classroom and student. Average fidelity was 57% in Strategies for Teaching based on Autism Research classrooms and 48% in Structured Teaching classrooms. There was a 9.2-point (standard deviation = 9.6) increase in Differential Ability Scales score over the 8-month study period, but no main effect of program. There was a significant interaction between fidelity and group. In classrooms with either low or high program fidelity, students in Strategies for Teaching based on Autism Research experienced a greater gain in Differential Ability Scales score than students in Structured Teaching (11.2 vs. 5.5 points and 11.3 vs. 8.9 points, respectively). In classrooms with moderate fidelity, students in Structured Teaching experienced a greater gain than students in Strategies for Teaching based on Autism Research (10.1 vs. 4.4 points). The results suggest significant variability in implementation of evidence-based practices, even with supports, and also suggest the need to address challenging issues related to implementation measurement in community settings.

Professionalism, fidelity and relationship-preservation: navigating disagreement and frustration in clinical encounters

In February 2012, The Wall Street Journal summarized cases and research documenting growth in the numbers of physicians who ask families to leave their practices due to parental refusal of vaccines for pediatric patients. (1) Some physicians ask families to leave because they feel that they have a professional obligation to maintain a standard of care that is unattainable when parents refuse vaccines for their children. Others struggle with how to maintain a therapeutic relationship with a child whose parents' health beliefs conflict with vaccine schedule recommendations. Additionally, one social and cultural trend that seems to influence physician-family relationships in these cases is "anti-intellectualism." I consider some important challenges these issues pose for professionalism in the physician-family relationship, and consider a few values helpful in configuring responses to those challenges.

Assessing fidelity of delivery of smoking cessation behavioural support in practice

BACKGROUND

Effectiveness of evidence-based behaviour change interventions is likely to be undermined by failure to deliver interventions as planned. Behavioural support for smoking cessation can be a highly cost-effective, life-saving intervention. However, in practice, outcomes are highly variable. Part of this may be due to variability in fidelity of intervention implementation. To date, there have been no published studies on this. The present study aimed to: evaluate a method for assessing fidelity of behavioural support; assess fidelity of delivery in two English Stop-Smoking Services; and compare the extent of fidelity according to session types, duration, individual practitioners, and component behaviour change techniques (BCTs).

METHODS

Treatment manuals and transcripts of 34 audio-recorded behavioural support sessions were obtained from two Stop-Smoking Services and coded into component BCTs using a taxonomy of 43 BCTs. Inter-rater reliability was assessed using percentage agreement. Fidelity was assessed by examining the proportion of BCTs specified in the manuals that were delivered in individual sessions. This was assessed by session type (i.e., pre-quit, quit, post-quit), duration, individual practitioner, and BCT.

RESULTS

Inter-coder reliability was high (87.1%). On average, 66% of manual-specified BCTs were delivered per session (SD 15.3, range: 35% to 90%). In Service 1, average fidelity was highest for post-quit sessions (69%) and lowest for pre-quit (58%). In Service 2, fidelity was highest for quit-day (81%) and lowest for post-quit sessions (56%). Session duration was not significantly correlated with fidelity. Individual practitioner fidelity ranged from 55% to 78%. Individual manual-specified BCTs were delivered on average 63% of the time (SD 28.5, range: 0 to 100%).

CONCLUSIONS

The extent to which smoking cessation behavioural support is delivered as specified in treatment manuals can be reliably assessed using transcripts of audiotaped sessions. This allows the investigation of the implementation of evidence-based practice in relation to smoking cessation, a first step in designing interventions to improve it. There are grounds for believing that fidelity in the English Stop-Smoking Services may be low and that routine monitoring is warranted.

Measuring Fidelity and Adaptation: Reliability of a Instrument for School-Based Prevention Programs

There is a need to standardize methods for assessing fidelity and adaptation. Such standardization would allow program implementation to be examined in a manner that will be useful for understanding the moderating role of fidelity in dissemination research. This article describes a method for collecting data about fidelity of implementation for school-based prevention programs, including measures of adherence, quality of delivery, dosage, participant engagement, and adaptation. We report about the reliability of these methods when applied by four observers who coded video recordings of teachers delivering All Stars, a middle school drug prevention program. Interrater agreement for scaled items was assessed for an instrument designed to evaluate program fidelity. Results indicated sound interrater reliability for items assessing adherence, dosage, quality of teaching, teacher understanding of concepts, and program adaptations. The interrater reliability for items assessing potential program effectiveness, classroom management, achievement of activity objectives, and adaptation valences was improved by dichotomizing the response options for these items. The item that assessed student engagement demonstrated only modest interrater reliability and was not improved through dichotomization. Several coder pairs were discordant on items that overall demonstrated good interrater reliability. Proposed modifications to the coding manual and protocol are discussed.

DNA polymerase delta in DNA replication and genome maintenance

The eukaryotic genome is in a constant state of modification and repair. Faithful transmission of the genomic information from parent to daughter cells depends upon an extensive system of surveillance, signaling, and DNA repair, as well as accurate synthesis of DNA during replication. Often, replicative synthesis occurs over regions of DNA that have not yet been repaired, presenting further challenges to genomic stability. DNA polymerase δ (pol δ) occupies a central role in all of these processes: catalyzing the accurate replication of a majority of the genome, participating in several DNA repair synthetic pathways, and contributing structurally to the accurate bypass of problematic lesions during translesion synthesis. The concerted actions of pol δ on the lagging strand, pol ϵ on the leading strand, associated replicative factors, and the mismatch repair (MMR) proteins results in a mutation rate of less than one misincorporation per genome per replication cycle. This low mutation rate provides a high level of protection against genetic defects during development and may prevent the initiation of malignancies in somatic cells. This review explores the role of pol δ in replication fidelity and genome maintenance.

Challenges in providing family-centered support to families in palliative care

BACKGROUND

Supporting the family-as-a-whole presents challenges in palliative care, although family meetings are increasingly used in routine practice. The Family Focused Grief Therapy (FFGT) Model guides clinicians in using a range of intervention strategies.

AIM

To examine the therapists' techniques used in assessing 'at risk' families in palliative care to better illuminate what helps and what remains challenging.

METHOD

Recorded sessions 1 and 2 were coded using the FFGT fidelity coding measure, with its glossary of definitions. Inter-rater reliability between three coders was satisfactory at 88%. Frequencies of strategy utilization were computed, with extraction of examples of both successful and problematic approaches.

SETTING/PARTICIPANTS

From within a larger study of family therapy during palliative care at a comprehensive cancer center, the first two sessions (n = 144) delivered to 74 families (299 individuals) by 32 therapists were coded and analyzed.

RESULTS

Therapists readily explored the story of illness and families' ways of coping (97%) and assessed communication and cohesiveness in the majority. Exploration of relational patterns occurred in 89% of sessions, use of a genogram in 80%, understanding members' roles in 65% and family values and beliefs in 62%. Less use was made of summaries (39%), family mottos (34%), exploration of family conflict (35%) and the formalization of a comprehensive family treatment plan (20%).

CONCLUSIONS

Challenges exist in therapy with difficult families. Therapy in the home brings special issues. Therapists can apply most of the interventions prescribed by the FFGT model.

Treatment fidelity in psychosocial intervention for children and adolescents with comorbid problems

BACKGROUND

  Intervention fidelity has important implications for the interpretation of intervention outcomes. Reviews on fidelity implementation for psychosocial interventions targeting children and adolescents with comorbid mental health problems are scarce. The purpose of this study was to systematically review reported fidelity of psychosocial interventions for children with comorbid mental health conditions.

METHOD

  Fidelity and quality ratings were calculated based on an analysis of articles resulting from a previously reported systematic search of the literature (using PsycINFO, MEDLINE and ERIC databases between 1994 and 2009), using the Intervention Fidelity Assessment Checklist for the fidelity measure and the Cochrane Collaboration's tool for assessing risk of bias for the quality measure.

RESULTS

  Overall, few studies were found to have a high level of fidelity adherence. Only 1 of the 10 studies met the 'high' intervention fidelity cutoff.

CONCLUSIONS

  Findings suggest that current psychosocial interventions for children and adolescents with comorbid mental health disorders must be interpreted with caution, given many studies either do not measure intervention fidelity or have variable levels of fidelity adherence. Including fidelity components in future studies would aid in determining the effectiveness and generalizability of interventions targeted at children with comorbid disorders.

Next Generation of the Java Image Science Toolkit (JIST): Visualization and Validation

Modern medical imaging analyses often involve the concatenation of multiple steps, and neuroimaging analysis is no exception. The Java Image Science Toolkit (JIST) has provided a framework for both end users and engineers to synthesize processing modules into tailored, automatic multi-step processing pipelines ("layouts") and rapid prototyping of module development. Since its release, JIST has facilitated substantial neuroimaging research and fulfilled much of its intended goal. However, key weaknesses must be addressed for JIST to more fully realize its potential and become accessible to an even broader community base. Herein, we identify three core challenges facing traditional JIST (JIST-I) and present the solutions in the next generation JIST (JIST-II). First, in response to community demand, we have introduced seamless data visualization; users can now click 'show this data' through the program interfaces and avoid the need to locating files on the disk. Second, as JIST is an open-source community effort by-design; any developer may add modules to the distribution and extend existing functionality for release. However, the large number of developers and different use cases introduced instability into the overal JIST-I framework, causing users to freeze on different, incompatible versions of JIST-I, and the JIST community began to fracture. JIST-II addresses the problem of compilation instability by performing continuous integration checks nightly to ensure community implemented changes do not negatively impact overall JIST-II functionality. Third, JIST-II allows developers and users to ensure that functionality is preserved by running functionality checks nightly using the continuous integration framework. With JIST-II, users can submit layout test cases and quality control criteria through a new GUI. These test cases capture all runtime parameters and help to ensure that the module produces results within tolerance, despite changes in the underlying architecture. These three "next generation" improvements increase the fidelity of the JIST framework and enhance utility by allowing researchers to more seamlessly and robustly build, manage, and understand medical image analysis processing pipelines.

Development and Initial Validation of a Client-Rated MET-CBT Adherence Measure

Traditional mechanisms for rating adherence or fidelity are labor-intensive. We developed and validated a tool to rate adherence to Motivational Enhancement Therapy—Cognitive Behavioral Treatment (MET-CBT) through anonymous client surveys. The instrument was used to survey clients in 3 methadone programs over 2 waves. Explanatory and Confirmatory Factor Analyses were used to establish construct validity for both MET and CBT. Internal consistency based on Cronbach’s alpha was within adequate range (α > 0.70) for all but 2 of the subscales in one of the samples. Consensus between clients’ ratings (r_wg(j) scores) were in the range of 0.6 and higher, indicating a moderate to strong degree of agreement among clients’ ratings of the same counselor. These results suggest that client surveys could be used to measure adherence to MET-CBT for quality monitoring that is more objective than counselor self-report and less resource-intensive than supervisor review of taped sessions. However, additional work is needed to develop this scale.

CEF1/CDC5 alleles modulate transitions between catalytic conformations of the spliceosome

Conformational change within the spliceosome is required between the first and second catalytic steps of pre-mRNA splicing. A prior genetic screen for suppressors of an intron mutant that stalls between the two steps yielded both prp8 and non-prp8 alleles that suppressed second-step splicing defects. We have now identified the strongest non-prp8 suppressors as alleles of the NTC (Prp19 complex) component, CEF1. These cef1 alleles generally suppress second-step defects caused by a variety of intron mutations, mutations in U6 snRNA, or deletion of the second-step protein factor Prp17, and they can activate alternative 3' splice sites. Genetic and functional interactions between cef1 and prp8 alleles suggest that they modulate the same event(s) in the first-to-second-step transition, most likely by stabilization of the second-step spliceosome; in contrast, alleles of U6 snRNA that also alter this transition modulate a distinct event, most likely by stabilization of the first-step spliceosome. These results implicate a myb-like domain of Cef1/CDC5 in interactions that modulate conformational states of the spliceosome and suggest that alteration of these events affects splice site use, resulting in alternative splicing-like patterns in yeast.

Mixed methods for implementation research: application to evidence-based practice implementation and staff turnover in community-based organizations providing child welfare services

Many public sector service systems and provider organizations are in some phase of learning about or implementing evidence-based interventions. Child welfare service systems represent a context where implementation spans system, management, and organizational concerns. Research utilizing mixed methods that combine qualitative and quantitative design, data collection, and analytic approaches are particularly well suited to understanding both the process and outcomes of dissemination and implementation efforts in child welfare systems. This article describes the process of using mixed methods in implementation research and provides an applied example of an examination of factors impacting staff retention during an evidence-based intervention implementation in a statewide child welfare system. The authors integrate qualitative data with previously published quantitative analyses of job autonomy and staff turnover during this statewide implementation project in order to illustrate the utility of mixed method approaches in providing a more comprehensive understanding of opportunities and challenges in implementation research.

Simulation and anaesthesia

Training in anaesthesia relies on the duration and quality of clinical experience. It involves exposure to a range of interventions. This works well in routine cases, but when an uncommon and life-threatening event occurs, the anaesthetist needs to carry out multiple tasks simultaneously. Aviation has remarkable similarities with the practice of anaesthesia. Over the years, the aviation industry has used simulation to train and assess individuals very effectively. Anaesthetists face rapidly evolving clinical situations. This needs appropriate decision-making and communication with others in the theatre team. Simulation, using current technology, offers innovative and reproducible training experience. It enables standardised scenario building and reflective learning. Various non-technical aspects of an anaesthetist's day-to-day work could also be addressed to during such training. The technology could be used very effectively for the assessment of competence too. Simulation has been used for technology development and appraisal over the years.

Judicious use of simulation technology in continuing medical education

Use of simulation-based training is fast becoming a vital source of experiential learning in medical education. Although simulation is a common tool for undergraduate and graduate medical education curricula, the utilization of simulation in continuing medical education (CME) is still an area of growth. As more CME programs turn to simulation to address their training needs, it is important to highlight concepts of simulation technology that can help to optimize learning outcomes. This article discusses the role of fidelity in medical simulation. It provides support from a cross section of simulation training domains for determining the appropriate levels of fidelity, and it offers guidelines for creating an optimal balance of skill practice and realism for efficient training outcomes. After defining fidelity, 3 dimensions of fidelity, drawn from the human factors literature, are discussed in terms of their relevance to medical simulation. From this, research-based guidelines are provided to inform CME providers regarding the use of simulation in CME training.

Implementing a Primary Prevention Social Skills Intervention in Urban Preschools: Factors Associated with Quality and Fidelity

RESEARCH FINDINGS: Preschool behavior problems are of increasing concern to early childhood educators. Preventive interventions are being developed, but implementation in under-resourced child care programs is challenging. This study describes the implementation of an adapted Second Step curriculum to increase children's social skills and decrease behavior problems in preschool classrooms. Teacher training/coaching, organizational supports, and procedures for sustainability are described. Measures included baseline classroom characteristics, lesson completion and fidelity, and teacher satisfaction. Teachers completed 88% of the lessons across two years. Follow-up monitoring in Year 3, once all training was terminated, found 95% of lessons were delivered with higher fidelity than the first two years. Teachers were satisfied with training, felt the curriculum improved children's social skills, and stated they would continue to use the curriculum. Lesson completion and fidelity were associated with various teacher characteristics, training attendance, classroom characteristics, teacher and child turnover, and the percent of children with developmental delays in the classroom. PRACTICE: Results support the implementation strategy and suggest that paying attention to teacher morale, general skill development, and a period of on-going support for training is important and will lead to sustainable and high implementation rates.

Detecting changes in real-world objects: The relationship between visual long-term memory and change blindness

A large body of literature has shown that observers often fail to notice significant changes in visual scenes, even when these changes happen right in front of their eyes. For instance, people often fail to notice if their conversation partner is switched to another person, or if large background objects suddenly disappear.1,2 These 'change blindness' studies have led to the inference that the amount of information we remember about each item in a visual scene may be quite low.1 However, in recent work we have demonstrated that long-term memory is capable of storing a massive number of visual objects with significant detail about each item.3 In the present paper we attempt to reconcile these findings by demonstrating that observers do not experience 'change blindness' with the real world objects used in our previous experiment if they are given sufficient time to encode each item. The results reported here suggest that one of the major causes of change blindness for real-world objects is a lack of encoding time or attention to each object (see also refs. 4 and 5).

Naturally occurring aminoacyl-tRNA synthetases editing-domain mutations that cause mistranslation in Mycoplasma parasites

Mycoplasma parasites escape host immune responses via mechanisms that depend on remarkable phenotypic plasticity. Identification of these mechanisms is of great current interest. The aminoacyl-tRNA synthetases (AARSs) attach amino acids to their cognate tRNAs, but occasionally make errors that substitute closely similar amino acids. AARS editing pathways clear errors to avoid mistranslation during protein synthesis. We show here that AARSs in Mycoplasma parasites have point mutations and deletions in their respective editing domains. The deleterious effect on editing was confirmed with a specific example studied in vitro. In vivo mistranslation was determined by mass spectrometric analysis of proteins produced in the parasite. These mistranslations are uniform cases where the predicted closely similar amino acid replaced the correct one. Thus, natural AARS editing-domain mutations in Mycoplasma parasites cause mistranslation. We raise the possibility that these mutations evolved as a mechanism for antigen diversity to escape host defense systems.

Distinct response of yeast ribosomes to a miscoding event during translation

Numerous mechanisms have evolved to control the accuracy of translation, including a recently discovered retrospective quality control mechanism in bacteria. This quality control mechanism is sensitive to perturbations in the codon:anticodon interaction in the P site of the ribosome that trigger a dramatic loss of fidelity in subsequent tRNA and release factor selection events in the A site. These events ultimately lead to premature termination of translation in response to an initial miscoding error. In this work, we extend our investigations of this mechanism to an in vitro reconstituted Saccharomyces cerevisiae translation system. We report that yeast ribosomes do not respond to mismatches in the P site by loss of fidelity in subsequent substrate recognition events. We conclude that retrospective editing, as initially characterized in Escherichia coli, does not occur in S. cerevisiae. These results highlight potential mechanistic differences in the functional core of highly conserved ribosomes.

Mutations of highly conserved bases in the peptidyltransferase center induce compensatory rearrangements in yeast ribosomes

Molecular dynamics simulation identified three highly conserved rRNA bases in the large subunit of the ribosome that form a three-dimensional (3D) "gate" that induces pausing of the aa-tRNA acceptor stem during accommodation into the A-site. A nearby fourth base contacting the "tryptophan finger" of yeast protein L3, which is involved in the coordinating elongation factor recruitment to the ribosome with peptidyltransfer, is also implicated in this process. To better understand the functional importance of these bases, single base substitutions as well as deletions at all four positions were constructed and expressed as the sole forms of ribosomes in yeast Saccharomyces cerevisiae. None of the mutants had strong effects on cell growth, translational fidelity, or on the interactions between ribosomes and tRNAs. However, the mutants did promote strong effects on cell growth in the presence of translational inhibitors, and differences in viability between yeast and Escherichia coli mutants at homologous positions suggest new targets for antibacterial therapeutics. Mutant ribosomes also promoted changes in 25S rRNA structure, all localized to the core of peptidyltransferase center (i.e., the proto-ribosome area). We suggest that a certain degree of structural plasticity is built into the ribosome, enabling it to ensure accurate translation of the genetic code while providing it with the flexibility to adapt and evolve.

Proofreading and spellchecking: a two-tier strategy for pre-mRNA splicing quality control

Multi-tier strategies exist in many biochemical processes to ensure a maximal fidelity of the reactions. In this review, we focus on the two-tier quality control strategy that ensures the quality of the products of the pre-mRNA splicing reactions catalyzed by the spliceosome. The first step in the quality control process relies on kinetic proofreading mechanisms that are internal to the spliceosome and that are performed by ATP-dependent RNA helicases. The second quality control step, spellchecking, involves recognition of unspliced pre-mRNAs or aberrantly spliced mRNAs that have escaped the first proofreading mechanisms, and subsequent degradation of these molecules by degradative enzymes in the nucleus or in the cytoplasm. This two-tier quality control strategy highlights a need for high fidelity and a requirement for degradative activities that eliminate defective molecules. The presence of multiple quality control activities during splicing underscores the importance of this process in the expression of genetic information.

Coronaviruses: an RNA proofreading machine regulates replication fidelity and diversity

In order to survive and propagate, RNA viruses must achieve a balance between the capacity for adaptation to new environmental conditions or host cells with the need to maintain an intact and replication competent genome. Several virus families in the order Nidovirales, such as the coronaviruses (CoVs) must achieve these objectives with the largest and most complex replicating RNA genomes known, up to 32 kb of positive-sense RNA. The CoVs encode sixteen nonstructural proteins (nsp 1-16) with known or predicted RNA synthesis and modification activities, and it has been proposed that they are also responsible for the evolution of large genomes. The CoVs, including murine hepatitis virus (MHV) and SARS-CoV, encode a 3'-to-5' exoribonuclease activity (ExoN) in nsp14. Genetic inactivation of ExoN activity in engineered SARS-CoV and MHV genomes by alanine substitution at conserved DE-D-D active site residues results in viable mutants that demonstrate 15- to 20-fold increases in mutation rates, up to 18 times greater than those tolerated for fidelity mutants of other RNA viruses. Thus nsp14-ExoN is essential for replication fidelity, and likely serves either as a direct mediator or regulator of a more complex RNA proofreading machine, a process previously unprecedented in RNA virus biology. Elucidation of the mechanisms of nsp14-mediated proofreading will have major implications for our understanding of the evolution of RNA viruses, and also will provide a robust model to investigate the balance between fidelity, diversity and pathogenesis. The discovery of a protein distinct from a viral RdRp that regulates replication fidelity also raises the possibility that RNA genome replication fidelity may be adaptable to differing replication environments and selective pressures, rather than being a fixed determinant.

The (human) science of medical virtual learning environments

The uptake of virtual simulation technologies in both military and civilian surgical contexts has been both slow and patchy. The failure of the virtual reality community in the 1990s and early 2000s to deliver affordable and accessible training systems stems not only from an obsessive quest to develop the 'ultimate' in so-called 'immersive' hardware solutions, from head-mounted displays to large-scale projection theatres, but also from a comprehensive lack of attention to the needs of the end users. While many still perceive the science of simulation to be defined by technological advances, such as computing power, specialized graphics hardware, advanced interactive controllers, displays and so on, the true science underpinning simulation--the science that helps to guarantee the transfer of skills from the simulated to the real--is that of human factors, a well-established discipline that focuses on the abilities and limitations of the end user when designing interactive systems, as opposed to the more commercially explicit components of technology. Based on three surgical simulation case studies, the importance of a human factors approach to the design of appropriate simulation content and interactive hardware for medical simulation is illustrated. The studies demonstrate that it is unnecessary to pursue real-world fidelity in all instances in order to achieve psychological fidelity--the degree to which the simulated tasks reproduce and foster knowledge, skills and behaviours that can be reliably transferred to real-world training applications.

Lesion bypass activity of DNA polymerase θ (POLQ) is an intrinsic property of the pol domain and depends on unique sequence inserts

DNA polymerase θ (POLQ, polθ) is a large, multidomain DNA polymerase encoded in higher eukaryotic genomes. It is important for maintaining genetic stability in cells and helping protect cells from DNA damage caused by ionizing radiation. POLQ contains an N-terminal helicase-like domain, a large central domain of indeterminate function, and a C-terminal polymerase domain with sequence similarity to the A-family of DNA polymerases. The enzyme has several unique properties, including low fidelity and the ability to insert and extend past abasic sites and thymine glycol lesions. It is not known whether the abasic site bypass activity is an intrinsic property of the polymerase domain or whether helicase activity is also required. Three "insertion" sequence elements present in POLQ are not found in any other A-family DNA polymerase, and it has been proposed that they may lend some unique properties to POLQ. Here, we analyzed the activity of the DNA polymerase in the absence of each sequence insertion. We found that the pol domain is capable of highly efficient bypass of abasic sites in the absence of the helicase-like or central domains. Insertion 1 increases the processivity of the polymerase but has little, if any, bearing on the translesion synthesis properties of the enzyme. However, removal of insertions 2 and 3 reduces activity on undamaged DNA and completely abrogates the ability of the enzyme to bypass abasic sites or thymine glycol lesions.

Examining implementer fidelity: Conceptualizing and measuring adherence and competence

The large gap between intervention outcomes demonstrated in efficacy trials and the apparent ineffectiveness of these same programs in community settings has prompted investigators and practitioners to look closely at implementation fidelity. Critically important, but often overlooked, are the implementers who deliver evidence-based programs -- the effectiveness of programs cannot surpass skill levels of the people implementing them. This article distinguishes fidelity at the programmatic level from implementer fidelity. Two components of implementer fidelity are defined. Implementer adherence and competence are proposed to be related but unique constructs that can be reliably measured for training¸ monitoring, and outcomes research. Observational measures from a school-based preventive intervention are provided and the unique contributions of implementer adherence and competence are illustrated. Distinguishing implementer adherence to the manual and competence in program delivery is a critical next step in child mental health program implementation research.

Three-year trajectory of teachers' fidelity to a drug prevention curriculum

Little is known about the trajectories over time of classroom teachers' fidelity to drug prevention curricula. Using the "Concerns-Based Adoption Model" (C-BAM) as a theoretical framework, we hypothesized that teachers' fidelity would improve with repetition. Participants comprised 23 middle school teachers who videotaped their administration of three entire iterations of the All Stars curriculum. Investigators coded two key curriculum lessons, specifically assessing the proportion of activities of each lesson teachers attempted and whether they omitted, added, or changed prescribed content, or delivered it using new methods. Study findings provided only partial support for the C-BAM model. Considerable variability in teachers' performance over time was noted, suggesting that their progression over time may be nonlinear and dynamic, and quite possibly a function of their classroom and school contexts. There was also evidence that, by their third iteration of All Stars, teachers tended to regress toward the baseline mean. That is, the implementation quality of those that started out with high levels of fidelity tended to degrade, while those that started out with very low fidelity to the curriculum tended to improve. Study findings suggest the need for ongoing training and technical assistance, as well as "just in time" messages delivered electronically; but it is also possible that some prevention curricula may impose unrealistic expectations or burdens on teachers' abilities and classroom time.

Mechanisms by which human DNA primase chooses to polymerize a nucleoside triphosphate

Human DNA primase synthesizes short RNA primers that DNA polymerase alpha then elongates during the initiation of all new DNA strands. Even though primase misincorporates NTPs at a relatively high frequency, this likely does not impact the final DNA product since the RNA primer is replaced with DNA. We used an extensive series of purine and pyrimidine analogues to provide further insights into the mechanism by which primase chooses whether or not to polymerize a NTP. Primase readily polymerized a size-expanded cytosine analogue, 1,3-diaza-2-oxophenothiazine NTP, across from a templating G but not across from A. The enzyme did not efficiently polymerize NTPs incapable of forming two Watson-Crick hydrogen bonds with the templating base with the exception of UTP opposite purine deoxyribonucleoside. Likewise, primase did not generate base pairs between two nucleotides with altered Watson-Crick hydrogen-bonding patterns. Examining the mechanism of NTP polymerization revealed that human primase can misincorporate NTPs via both template misreading and a primer-template slippage mechanism. Together, these data demonstrate that human primase strongly depends on Watson-Crick hydrogen bonds for efficient nucleotide polymerization, much more so than the mechanistically related herpes primase, and provide insights into the potential roles of primer-template stability and base tautomerization during misincorporation.

Mutation rates and intrinsic fidelity of retroviral reverse transcriptases

Retroviruses are RNA viruses that replicate through a DNA intermediate, in a process catalyzed by the viral reverse transcriptase (RT). Although cellular polymerases and host factors contribute to retroviral mutagenesis, the RT errors play a major role in retroviral mutation. RT mutations that affect the accuracy of the viral polymerase have been identified by in vitro analysis of the fidelity of DNA synthesis, by using enzymological (gel-based) and genetic assays (e.g., M13mp2 lacZ forward mutation assays). For several amino acid substitutions, these observations have been confirmed in cell culture using viral vectors. This review provides an update on studies leading to the identification of the major components of the fidelity center in retroviral RTs.

Exposure to Adolescent Community Reinforcement Approach treatment procedures as a mediator of the relationship between adolescent substance abuse treatment retention and outcome

Data from 399 adolescents, who participated in one of four randomly controlled trials of the Adolescent Community Reinforcement Approach (A-CRA) intervention, were used to examine the extent to which exposure to A-CRA procedures mediated the relationship between treatment retention and outcomes. Although zero-order correlations indicated that retention in treatment was a significant predictor of alcohol and other drug (AOD) use (r = -0.18, p < .001), this relationship was reduced to nonsignificance (p = .39) when exposure to A-CRA procedures was included in the model. Overall, the final model evidenced a very good fit (root mean square error of approximation = .00; comparative fit index = 1.00) and explained 29% and 43% of the variance in adolescents' posttreatment AOD use and AOD-related problems, respectively. In addition, Chi-Squared Automatic Interaction Detection analysis was used to derive a target level of A-CRA exposure, which was found to be significantly related to being in recovery at follow-up. The current findings are useful, as little research to date has identified significant mediators of the relationship between retention and treatment outcomes or identified target thresholds of treatment exposure.

Visual long-term memory has a massive storage capacity for object details

One of the major lessons of memory research has been that human memory is fallible, imprecise, and subject to interference. Thus, although observers can remember thousands of images, it is widely assumed that these memories lack detail. Contrary to this assumption, here we show that long-term memory is capable of storing a massive number of objects with details from the image. Participants viewed pictures of 2,500 objects over the course of 5.5 h. Afterward, they were shown pairs of images and indicated which of the two they had seen. The previously viewed item could be paired with either an object from a novel category, an object of the same basic-level category, or the same object in a different state or pose. Performance in each of these conditions was remarkably high (92%, 88%, and 87%, respectively), suggesting that participants successfully maintained detailed representations of thousands of images. These results have implications for cognitive models, in which capacity limitations impose a primary computational constraint (e.g., models of object recognition), and pose a challenge to neural models of memory storage and retrieval, which must be able to account for such a large and detailed storage capacity.

Multiple functions of DNA polymerases

The primary role of DNA polymerases is to accurately and efficiently replicate the genome in order to ensure the maintenance of the genetic information and its faithful transmission through generations. This is not a simple task considering the size of the genome and its constant exposure to endogenous and environmental DNA damaging agents. Thus, a number of DNA repair pathways operate in cells to protect the integrity of the genome. In addition to their role in replication, DNA polymerases play a central role in most of these pathways. Given the multitude and the complexity of DNA transactions that depend on DNA polymerase activity, it is not surprising that cells in all organisms contain multiple highly specialized DNA polymerases, the majority of which have only recently been discovered. Five DNA polymerases are now recognized in Escherichia coli, 8 in Saccharomyces cerevisiae, and at least 15 in humans. While polymerases in bacteria, yeast and mammalian cells have been extensively studied much less is known about their counterparts in plants. For example, the plant model organism Arabidopsis thaliana is thought to contain 12 DNA polymerases, whose functions are mostly unknown. Here we review the properties and functions of DNA polymerases focusing on yeast and mammalian cells but paying special attention to the plant enzymes and the special circumstances of replication and repair in plant cells.

Probing the active site tightness of DNA polymerase in subangstrom increments

We describe the use of a series of gradually expanded thymine nucleobase analogs in probing steric effects in DNA polymerase efficiency and fidelity. In these nonpolar compounds, the base size was increased incrementally over a 1.0-A range by use of variably sized atoms (H, F, Cl, Br, and I) to replace the oxygen molecules of thymine. Kinetics studies with DNA Pol I (Klenow fragment, exonuclease-deficient) in vitro showed that replication efficiency opposite adenine increased through the series, reaching a peak at the chlorinated compound. Efficiency then dropped markedly as a steric tightness limit was apparently reached. Importantly, fidelity also followed this trend, with the fidelity maximum at dichlorotoluene, the largest compound that fits without apparent repulsion. The fidelity at this point approached that of wild-type thymine. Surprisingly, the maximum fidelity and efficiency was found at a base pair size significantly larger than the natural size. Parallel bypass and mutagenesis experiments were then carried out in vivo with a bacterial assay for replication. The cellular results were virtually the same as those seen in solution. The results provide direct evidence for the importance of a tight steric fit on DNA replication fidelity. In addition, the results suggest that even high-fidelity replicative enzymes have more steric room than necessary, possibly to allow for an evolutionarily advantageous mutation rate.

Regulation of 5' template usage and incorporation of noncognate nucleotides by human telomerase

Telomerase accurately synthesizes telomeric DNA by reverse transcription of a tightly defined template region in the telomerase RNA (TR). Reverse transcription past the 5' boundary of the template can cause the incorporation of noncognate nucleotides into telomeric DNA, which can result in disruption of normal telomere function. The products synthesized by human telomerase do not contain the nucleotide cytosine, which is encoded by an hTR residue 2 nucleotides (nt) 5' of the template boundary. We examined dCTP incorporation by a series of telomerases reconstituted with N- and C-terminally mutated human telomerase reverse transcriptases (hTERTs). We found that altering sequences in the N-terminal RNA interaction domain 1 (RID1) and C terminus caused dCTP-dependent catalytic phenotypes suggestive of reverse transcription of sequences 5' of the template boundary. A RID1 mutant that exhibited a dCTP-dependent phenotype interacted less efficiently with a human telomerase RNA (hTR) variant in which the 5' template boundary-defining P1b element was disrupted, whereas C-terminal mutations did not alter hTR interactions in a P1b-dependent fashion. Disruption of P1b or template linker sequences between P1b and the 5' template boundary also impaired 5' template usage in RID1 and C-terminal hTERT mutants. These observations identify overlapping roles for hTR sequences and structures 5' of the template in regulating both 5' template boundary definition and 5' template usage, and implicate hTERT N- and C-terminal regions in 5' template usage and suppression of noncognate nucleotide incorporation.

5S rRNA: Structure and Function from Head to Toe

5S rRNA is uniquely positioned so as to link together all of the functional centers of the ribosome. Previous studies have supported the hypothesis that 5S rRNA acts as a physical transducer of information, facilitating communication between the different functional centers and coordinating of the multiple events catalyzed by the ribosome. Here, we present a synthesis of both structural and genetic information to construct a more detailed picture of how 5S rRNA may act to transmit and coordinate all of the functional centers of the ribosome.

5S rRNA: Structure and Function from Head to Toe

5S rRNA is uniquely positioned so as to link together all of the functional centers of the ribosome. Previous studies have supported the hypothesis that 5S rRNA acts as a physical transducer of information, facilitating communication between the different functional centers and coordinating of the multiple events catalyzed by the ribosome. Here, we present a synthesis of both structural and genetic information to construct a more detailed picture of how 5S rRNA may act to transmit and coordinate all of the functional centers of the ribosome.

Dysfunctional proofreading in the Escherichia coli DNA polymerase III core

The epsilon-subunit contains the catalytic site for the 3'-->5' proofreading exonuclease that functions in the DNA pol III (DNA polymerase III) core to edit nucleotides misinserted by the alpha-subunit DNA pol. A novel mutagenesis strategy was used to identify 23 dnaQ alleles that exhibit a mutator phenotype in vivo. Fourteen of the epsilon mutants were purified, and these proteins exhibited 3'-->5' exonuclease activities that ranged from 32% to 155% of the activity exhibited by the wild-type epsilon protein, in contrast with the 2% activity exhibited by purified MutD5 protein. DNA pol III core enzymes constituted with 11 of the 14 epsilon mutants exhibited an increased error rate during in vitro DNA synthesis using a forward mutation assay. Interactions of the purified epsilon mutants with the alpha- and theta;-subunits were examined by gel filtration chromatography and exonuclease stimulation assays, and by measuring polymerase/exonuclease ratios to identify the catalytically active epsilon511 (I170T/V215A) mutant with dysfunctional proofreading in the DNA pol III core. The epsilon511 mutant associated tightly with the alpha-subunit, but the exonuclease activity of epsilon511 was not stimulated in the alpha-epsilon511 complex. Addition of the theta;-subunit to generate the alpha-epsilon511-theta; DNA pol III core partially restored stimulation of the epsilon511 exonuclease, indicating a role for the theta;-subunit in co-ordinating the alpha-epsilon polymerase-exonuclease interaction. The alpha-epsilon511-theta; DNA pol III core exhibited a 3.5-fold higher polymerase/exonuclease ratio relative to the wild-type DNA pol III core, further indicating dysfunctional proofreading in the alpha-epsilon511-theta; complex. Thus the epsilon511 mutant has wild-type 3'-->5' exonuclease activity and associates physically with the alpha- and theta;-subunits to generate a proofreading-defective DNA pol III enzyme.

The fidelity of replication of the three-base-pair set adenine/thymine, hypoxanthine/cytosine and 6-thiopurine/5-methyl-2-pyrimidinone with T7 DNA polymerase

With the goal of constructing a genetic alphabet consisting of a set of three base pairs, the fidelity of replication of the three base pairs T(H) (5-methyl-2-pyrimidinone)/H(S) (6-thiopurine; thiohypoxanthine), C/H (hypoxanthine) and T/A was evaluated using T7 DNA polymerase, a polymerase with a strong 3'-->5' exonuclease activity. An evaluation of the suitability of a new base pair for replication should include both the contribution of the fidelity of a polymerase activity and the contribution of proofreading by a 3'-->5' exonuclease activity. Using a steady-state kinetics method that included the contribution of the 3'-->5' exonuclease activity, the fidelity of replication was determined. The method determined the ratio of the apparent rate constant for the addition of a deoxynucleotide to the primer across from a template base by the polymerase activity and the rate constant for removal of the added deoxynucleotide from the primer by the 3'-->5' exonuclease activity. This ratio was designated the eni (efficiency of net incorporation). The eni of the base pair C/H was equal to or greater than the eni of T/A. The eni of the base pair T(H)/H(S) was 0.1 times that of A/T for T(H) in the template and 0.01 times that of A/T for H(S) in the template. The ratio of the eni of a mismatched deoxynucleotide to the eni of a matched deoxynucleotide was a measure of the error frequency. The error frequencies were as follows: thymine or T(H) opposite a template hypoxanthine, 2x10(-6); H(S) opposite a template cytosine, <3x10(-4). The remaining 24 mismatched combinations of bases gave no detectable net incorporation. Two mismatches, hypoxanthine opposite a template thymine or a template T(H), showed trace incorporation in the presence of a standard dNTP complementary to the next template base. T7 DNA polymerase extended the primer beyond each of the matched base pairs of the set. The level of fidelity of replication of the three base pairs with T7 DNA polymerase suggests that they are adequate for a three-base-pair alphabet for DNA replication.

Mismatch extension during strong stop strand transfer and minimal homology requirements for replicative template switching during Moloney murine leukemia virus replication

Reverse transcription requires two replicative template switches, called minus and plus strand strong stop transfer, and can include additional, recombinogenic switches. Donor and acceptor template homology facilitates both replicative and recombinogenic transfers, but homology-independent determinants may also contribute. Here, improved murine leukemia virus-based assays were established and the effects of varying extents of mismatches and complementarity between primer and acceptor template regions were assessed. Template switch accuracy was addressed by examining provirus structures, and efficiency was measured using a competitive titer assay. The results demonstrated that limited mismatch extension occurred readily during both minus and plus strand transfer. A strong bias for correct targeting to the U3/R junction and against use of alternate regions of homology was observed during minus strand transfer. Transfer to the U3/R junction was as accurate with five bases of complementarity as it was with an intact R, and as few as 3nt targeted transfer to a limited extent. In contrast, 12 base recombinogenic acceptors were utilized poorly and no accurate switch was observed when recombination acceptors retained only five bases of complementarity. These findings confirm that murine leukemia virus replicative and recombinogenic template switches differ in homology requirements, and support the notion that factors other than primer-template complementarity may contribute to strong stop acceptor template recognition.

Perceived fidelity of compressed and reconstructed radiological images: a preliminary exploration of compression, luminance, and viewing distance

The authors' goal was to explore the impact of image compression algorithm and ratio, image luminance, and viewing distance on radiologists' perception of reconstructed image fidelity. Five radiologists viewed 16 sets of four hard-copy chest radiographs prepared for secondary interpretation. Each set included one uncompressed, and three compressed and reconstructed images prepared using three different algorithms but the same compression ratio. The sets were prepared using two subjects, four compression ratios (10:1, 20:1, 30:1, 40:1), and two luminance levels (2,400 cd/m2, standard lightbox illumination, and 200 cd/m2, simulating a typical CRT display). Readers ranked image quality and evaluated obviousness and clinical importance of differences. Viewing distances for image screening, inspection, and comparison were recorded. At 10:1 compression, the compressed and uncompressed images were nearly indistinguishable; the three algorithms were very similar, and differences were rated "not obvious" and "not important." At higher compression, readers consistently preferred uncompressed images, with notable differences between algorithms. The obviousness and clinical importance of differences were rated higher at lightbox luminance. Viewing distances appeared to be idiosyncratic.