Surgeon Sex and Health Care Costs for Patients Undergoing Common Surgical Procedures

Importance

Prior research has shown differences in postoperative outcomes for patients treated by female and male surgeons. It is important to understand, from a health system and payer perspective, whether surgical health care costs differ according to the surgeon's sex.

Objective

To examine the association between surgeon sex and health care costs among patients undergoing surgery.

Design, Setting, and Participants

This population-based, retrospective cohort study included adult patients undergoing 1 of 25 common elective or emergent surgical procedures between January 1, 2007, and December 31, 2019, in Ontario, Canada. Analysis was performed from October 2022 to March 2023.

Exposure

Surgeon sex.

Main Outcome and Measure

The primary outcome was total health care costs assessed 1 year following surgery. Secondarily, total health care costs at 30 and 90 days, as well as specific cost categories, were assessed. Generalized estimating equations were used with procedure-level clustering to compare costs between patients undergoing equivalent surgeries performed by female and male surgeons, with further adjustment for patient-, surgeon-, anesthesiologist-, hospital-, and procedure-level covariates.

Results

Among 1 165 711 included patients, 151 054 were treated by a female surgeon and 1 014 657 were treated by a male surgeon. Analyzed at the procedure-specific level and accounting for patient-, surgeon-, anesthesiologist-, and hospital-level covariates, 1-year total health care costs were higher for patients treated by male surgeons ($24 882; 95% CI, $20 780-$29 794) than female surgeons ($18 517; 95% CI, $16 080-$21 324) (adjusted absolute difference, $6365; 95% CI, $3491-9238; adjusted relative risk, 1.10; 95% CI, 1.05-1.14). Similar patterns were observed at 30 days (adjusted absolute difference, $3115; 95% CI, $1682-$4548) and 90 days (adjusted absolute difference, $4228; 95% CI, $2255-$6202).

Conclusions and Relevance

This analysis found lower 30-day, 90-day, and 1-year health care costs for patients treated by female surgeons compared with those treated by male surgeons. These data further underscore the importance of creating inclusive policies and environments supportive of women surgeons to improve recruitment and retention of a more diverse and representative workforce.

Stable rates of operative treatment of distal radius fractures in Ontario, Canada: a population-based retrospective cohort study (2004–2013)

Background

Rates of surgical management of distal radius fractures are increasing internationally despite the higher cost and limited outcome evidence to support this shift. This study examines the epidemiology of distal radius fractures and asks if the same shift has occurred in Ontario, Canada (population 13.9 million).

Methods

This population-based, retrospective cohort study examined distal radius fractures in people aged 18 years and older over a 10-year period (2004–2013). The incidence analyses were based on the first occurrence of a fracture within a 2-year time period. The number of fractures, age-adjusted incidence rates and frequency of fracture treatment type by year were assessed. We used a Poisson regression with robust standard errors to determine if there was a statistically significant change in the frequency of fracture treatment type over time.

Results

There were 25 355 distal radius fractures among Ontarians 18 years of age and older in 2013. Between 2004 and 2013, the age-adjusted incidence rate for people 35 years of age and older was stable, between 2.32 and 2.70 per 1000 population. Rates of cast immobilization remained stable between 82% and 84%. Of those patients treated surgically, the rate of open reduction and internal fixation rose from 7% in 2004 to 13% in 2013 at the expense of other types of surgical management.

Conclusion

In Ontario, rates of cast immobilization are stable and there has been a movement toward open reduction and internal fixation among patients treated surgically.

Effect of Home Monitoring via Mobile App on the Number of In-Person Visits Following Ambulatory Surgery: A Randomized Clinical Trial

Importance

In the age of information and patient-centered care, new methods of delivering postoperative care must be developed and evaluated.

Objective

To determine whether follow-up care delivered via a mobile app can be used to avert in-person follow-up care visits compared with conventional, in-person follow-up care in the first 30 days following ambulatory surgery.

Design, Setting, and Participants

A randomized clinical trial was conducted from February 1 to August 31, 2015, among ambulatory patients undergoing breast reconstruction at an academic ambulatory care hospital. Patients were randomly assigned to receive follow-up care via a mobile app or at an in-person visit during the first 30 days after the operation. Analysis was intention-to-treat.

Main Outcomes and Measures

The primary end point was the number of in-person follow-up visits during the first 30 days after the operation. Secondary end points were the number of telephone calls and emails to health care professionals, patient-reported convenience and satisfaction scores, and rates of complications.

Results

Of the 65 women in the study (mean [SD] age, 47.7 [13.4] years), 32 (49%) were in the mobile app group, and 33 (51%) were in the in-person follow-up care group. Those in the mobile app group attended a mean of 0.66 in-person visits, vs 1.64 in-person visits in the in-person follow-up care group, for a difference of 0.40 times fewer in-person visits (95% CI, 0.24-0.66; P < .001) and sent more emails to their health care professionals during the first 30 days after the operation (mean, 0.65 vs 0.15; incidence rate ratio, 4.13; 95% CI, 1.55-10.99; P = .005) than did patients in the in-person follow-up care group. This statistically significant difference was maintained at 3 months postoperatively. The mobile app group reported higher convenience scores than the in-person follow-up care group (incidence rate ratio, 1.39; 95% CI, 1.09-1.77; P = .008). There was no difference between groups in the number of telephone communications, satisfaction scores, or complication rates.

Conclusions and Relevance

Patients undergoing ambulatory breast reconstruction can use follow-up care via a mobile app to avert in-person follow-up visits during the first 30 days after the operation. Mobile app follow-up care affects neither complication rates nor patient-reported satisfaction scores, but it improves patient-reported convenience scores.

Trial Registration

clinicaltrials.gov Identifier: NCT02318953.

Sleep-related crash characteristics: Implications for applying a fatigue definition to crash reports

Sleep-related (SR) crashes are an endemic problem the world over. However, police officers report difficulties in identifying sleepiness as a crash contributing factor. One approach to improving the sensitivity of SR crash identification is by applying a proxy definition post hoc to crash reports. To identify the prominent characteristics of SR crashes and highlight the influence of proxy definitions, ten years of Queensland (Australia) police reports of crashes occurring in ≥100km/h speed zones were analysed. In Queensland, two approaches are routinely taken to identifying SR crashes. First, attending police officers identify crash causal factors; one possible option is 'fatigue/fell asleep'. Second, a proxy definition is applied to all crash reports. Those meeting the definition are considered SR and added to the police-reported SR crashes. Of the 65,204 vehicle operators involved in crashes 3449 were police-reported as SR. Analyses of these data found that male drivers aged 16-24 years within the first two years of unsupervised driving were most likely to have a SR crash. Collision with a stationary object was more likely in SR than in not-SR crashes. Using the proxy definition 9739 (14.9%) crashes were classified as SR. Using the proxy definition removes the findings that SR crashes are more likely to involve males and be of high severity. Additionally, proxy defined SR crashes are no less likely at intersections than not-SR crashes. When interpreting crash data it is important to understand the implications of SR identification because strategies aimed at reducing the road toll are informed by such data. Without the correct interpretation, funding could be misdirected. Improving sleepiness identification should be a priority in terms of both improvement to police and proxy reporting.

Sleep-related vehicle crashes on low speed roads

BACKGROUND

Very little is known about the characteristics of sleep related (SR) crashes occurring on low speed roads compared with current understanding of the role of sleep in crashes occurring on high speed roads e.g. motorways. To address this gap, analyses were undertaken to identify the differences and similarities between (1) SR crashes occurring on roads with low (≤60km/h) and high (≥100km/h) speed limits, and (2) SR crashes and not-SR crashes occurring on roads with low speed limits.

METHOD

Police reports of all crashes occurring on low and high speed roads over a ten year period between 2000 and 2009 were examined for Queensland, Australia. Attending police officers identified all crash attributes, including 'fatigue/fell asleep', which indicates that the police believe the crash to have a causal factor relating to falling asleep, sleepiness due to sleep loss, time of day, or fatigue. Driver or rider involvement in crashes was classified as SR or not-SR. All crash-associated variables were compared using Chi-square tests (Cramer's V=effect size). A series of logistic regression was performed, with driver and crash characteristics as predictors of crash category. A conservative alpha level of 0.001 determined statistical significance.

RESULTS

There were 440,855 drivers or riders involved in a crash during this time; 6923 (1.6%) were attributed as SR. SR crashes on low speed roads have similar characteristics to those on high speed roads with young (16-24y) males consistently over represented. SR crashes on low speed roads are noticeably different to not-SR crashes in the same speed zone in that male and young novice drivers are over represented and outcomes are more severe. Of all the SR crashes identified, 41% occurred on low speed roads.

CONCLUSION

SR crashes are not confined to high speed roads. Low speed SR crashes warrant specific investigation because they occur in densely populated areas, exposing a greater number of people to risk and have more severe outcomes than not-SR crashes on the same low speed roads.

The effect of mobile app home monitoring on number of in-person visits following ambulatory surgery: protocol for a randomized controlled trial

Background

Women’s College Hospital, Toronto, Canada, offers specialized ambulatory surgical procedures. Patients often travel great distances to undergo surgery. Most patients receiving ambulatory surgery have a low rate of postoperative events necessitating clinic visits. However, regular follow-up is still considered important in the early postoperative phase. Increasingly, telemedicine is used to overcome the distance patients must travel to receive specialized care. Telemedicine data suggest that mobile monitoring and follow-up care is valued by patients and can reduce costs to society. Women’s College Hospital has used a mobile app (QoC Health Inc) to complement in-person postoperative follow-up care for breast reconstruction patients. Preliminary studies suggest that mobile app follow-up care is feasible, can avert in-person follow-up care, and is cost-effective from a societal and health care system perspective.

Objective

We hope to expand the use of mobile app follow-up care through its formal assessment in a randomized controlled trial. In postoperative ambulatory surgery patients at Women’s College Hospital (WCH), can we avert in-person follow-up care through the use of mobile app follow-up care compared to conventional, in-person follow-up care in the first 30 days after surgery.

Methods

This will be a pragmatic, single-center, open, controlled, 2-arm parallel-group superiority randomized trial comparing mobile app and in-person follow-up care over the first month following surgery. The patient population will comprise all postoperative ambulatory surgery patients at WCH undergoing breast reconstruction. The intervention consists of a postoperative mobile app follow-up care using the quality of recovery-9 (QoR9) and a pain visual analog scale (VAS), surgery-specific questions, and surgical site photos submitted daily for the first 2 weeks and weekly for the following 2 weeks. The primary outcome is the total number of physician visits related to the surgery over the first 30-days postoperative. The secondary outcomes include (1) the total number of phone calls and emails to a health care professional related to surgery, (2) complication rate, (3) societal and health care system costs, and (4) patient satisfaction over the first 30 days postoperative. Permutated-block randomization will be conducted by blocks of 4-6 using the program ralloc in Stata. This is an open study due to the nature of the intervention.

Results

A sample of 72 (36 patients per group) will provide an E-test for count data with a power of 95% (P=.05) to detect a difference of 1 visit between groups, assuming a 10% drop out rate. Count variables will be analyzed using Poisson regression. Categorical variables will be tested using a chi-square test. Cost-effectiveness will be analyzed using net benefit regression. Outcomes will be assessed over the first 30 days following surgery.

Conclusions

We hope to show that the use of a mobile app in follow-up care minimizes the need for in-person visits for postoperative patients.

Trial Registration

Clinicaltrials.gov NCT02318953; https://clinicaltrials.gov/ct2/show/NCT02318953 (Archived by WebCite at http://www.webcitation.org/6Yifzdjph).

Replacing ambulatory surgical follow-up visits with mobile app home monitoring: modeling cost-effective scenarios

Background

Women’s College Hospital (WCH) offers specialized surgical procedures, including ambulatory breast reconstruction in post-mastectomy breast cancer patients. Most patients receiving ambulatory surgery have low rates of postoperative events necessitating clinic visits. Increasingly, mobile monitoring and follow-up care is used to overcome the distance patients must travel to receive specialized care at a reduced cost to society. WCH has completed a feasibility study using a mobile app (QoC Health Inc, Toronto) that suggests high patient satisfaction and adequate detection of postoperative complications.

Objective

The proposed cost-effectiveness study models the replacement of conventional, in-person postoperative follow-up care with mobile app follow-up care following ambulatory breast reconstruction in post-mastectomy breast cancer patients.

Methods

This is a societal perspective cost-effectiveness analysis, wherein all costs are assessed irrespective of the payer. The patient/caregiver, health care system, and externally borne costs are calculated within the first postoperative month based on cost information provided by WCH and QoC Health Inc. The effectiveness of telemedicine and conventional follow-up care is measured as successful surgical outcomes at 30-days postoperative, and is modeled based on previous clinical trials containing similar patient populations and surgical risks.

Results

This costing assumes that 1000 patients are enrolled in bring-your-own-device (BYOD) mobile app follow-up per year and that 1.64 in-person follow-ups are attended in the conventional arm within the first month postoperatively. The total cost difference between mobile app and in-person follow-up care is $245 CAD ($223 USD based on the current exchange rate), with in-person follow-up being more expensive ($381 CAD) than mobile app follow-up care ($136 CAD). This takes into account the total of health care system, patient, and external borne costs. If we examine health care system costs alone, in-person follow-up is $38 CAD ($35 USD) more expensive than mobile app follow-up care over the first postoperative month. The baseline difference in effect is modeled to be zero based on clinical trials examining the effectiveness of telephone follow-up care in similar patient populations. An incremental cost-effectiveness ratio (ICER) is not reportable in this scenario. An incremental net benefit (INB) is reportable, and reflects merely the cost difference between the two interventions for any willingness-to-pay value (INB=$245 CAD). The cost-effectiveness of mobile app follow-up even holds in scenarios where all mobile patients attend one in-person follow-up.

Conclusions

Mobile app follow-up care is suitably targeted to low-risk postoperative ambulatory patients. It can be cost-effective from a societal and health care system perspective.

Effect of aggressive risk factor modification on cardiac events and myocardial ischaemia in patients with chronic kidney disease

OBJECTIVE

To examine whether aggressive risk factor modification in chronic kidney disease (CKD) can limit the development of new ischaemia or reduce cardiac events.

METHODS

Patients with CKD were randomly assigned to either an aggressive risk factor modification strategy (targeted treatment of hypertension, dyslipidaemia, homocysteine, haemoglobin and phosphate) or standard care. An intention to treat analysis was performed on 152 patients who had baseline dobutamine stress echocardiography (DSE), including 107 who had follow-up DSE. Biochemical parameters, cardiac risk factors and investigations (ECG, two-dimensional echocardiography) were recorded at baseline. New ischaemia was classed as new or worsening stress wall motion abnormality between follow-up and baseline DSE. Patients were followed up for the development of new ischaemia or cardiac death, acute coronary syndrome and non-fatal myocardial infarction over 1.8 years.

RESULTS

The development of new ischaemia was common but not different between the standard and aggressively treated groups (15 (21%) v 18 (23%), p = 0.8). Independent predictors of new ischaemia were older age, abnormal ECG, higher systolic blood pressure and lower serum high density lipoprotein cholesterol, but not treatment arm. The standard and aggressively treated groups did not differ in cardiac event rate (10% v 13%, p = 0.6) or all-cause mortality (10% v 19%, p = 0.2). In patients with an abnormal baseline DSE (non-diagnostic, scar or ischaemia), the event rate was similar (22% v 20%, p = 0.9).

CONCLUSION

Aggressive risk factor modification in CKD does not limit the development of new ischaemia or reduce cardiac events in patients with an abnormal DSE.

Reproductive health needs: comparing women at high, drug-related risk of HIV with a national sample

Women who inject drugs or have injection drug-using sex partners are at high risk of acquiring human immunodeficiency virus (HIV) infection and of transmitting HIV perinatally. Many of these women need standard reproductive health care services, specialized HIV care, pre- and postnatal care, and drug treatment, but the extent of the unmet need for such health services is unknown. Large-scale national surveys that estimate drug use do not include reproductive health topics and vice versa. In addition, such surveys typically employ a household sampling method that tends not to include drug-using women. This paper presents evidence from three convenience samples that a high-risk population of women who use drugs has limited access to reproductive health services, and that this population is not represented in the National Survey of Family Growth (NSFG), the national survey that informs public policy regarding reproductive health care in the United States. Policy makers would be well served by regular surveillance of the multiple service needs of women with HIV-risk-related behaviors.

Ten-year follow-up of ovarian cancer patients after second-look laparotomy with negative findings

OBJECTIVE

To determine long-term survival and predictors of recurrence in patients with platinum-treated ovarian cancer who were followed for 10 years after second-look laparotomy with negative findings.

METHODS

Records were reviewed of 91 consecutive patients with negative findings on second-look laparotomy after platinum-based chemotherapy between January 1978 and January 1987. Statistical analysis used Kaplan-Meier survival curves, Cox proportional hazards, and multiple logistic regression.

RESULTS

Mean age of patients was 57 (range 30-79) years. Distribution by stage and grade was as follows: stage I, ten; II, 18; III, 57; IV, six; grade 1, 18; 2, 28; 3, 45. Forty-seven of 91 women had optimal initial cytoreduction. Recurrence-free survival rates for all subjects were 75% at 2 years, 55% at 5 years, and 52% at 10 years. For women with stage I disease, the recurrence-free survival rate was 90% at 2, 5, and 10 years. For women with stage II disease, recurrence-free survival rates were 78, 72, and 66% at 2, 5, and 10 years, respectively. Patients with stage III or IV disease had recurrence-free survival rates of 72, 44, and 40% at 2, 5, and 10 years, respectively. Risk of recurrent disease was related to tumor stage (relative risk [RR] 2.02; 95% confidence interval [CI] 1.2, 3.3; P = .005), grade (RR 2.00; 95% CI 1.3, 3.2; P = .004), and presence of a residual tumor of more than 2 cm at the end of initial surgery (RR 3.19; 95% CI 1.2, 8.5; P = .02).

CONCLUSION

Ovarian cancer patients face an appreciable risk of recurrence in the first 5 years after second-look laparotomy with negative findings after platinum-based chemotherapy, but those who remain disease free at 5 years have excellent long-term survival rates. Tumor stage, grade, and presence of a residual tumor of more than 2 cm after initial surgery are significant predictors of recurrence.

Results of a domestic violence training program offered to the staff of urban community health centers. Evaluation Committee of the Philadelphia Family Violence Working Group

INTRODUCTION

Domestic violence (DV) against women often goes unrecognized by health care providers due to multiple barriers. In an effort to increase screening, identification, and referral for services, the RADAR Training Project was created for the health care staff of 12 federally qualified community health centers (CHCs).

METHODS

A two-phase evaluation was conducted to assess the intervention. Phase one evaluated the health care providers' perceived knowledge and comfort pre-training, post-training, and at 3 months follow-up. The second phase included a medical chart review of 4 CHCs to assess the rates of screening, documentation of abuse, assessment of safety, and referrals for help at baseline (6 months pre-training) as compared to the intervention period (6 months post-training).

RESULTS

The health care providers' perceived level of knowledge and comfort increased significantly post-training and then later decreased at 3 months follow-up. The rate of screening for DV (25% vs. 5%), suspicion of DV (6% vs. 2%), completion of safety assessments (17% vs. 5%), and referrals (4% vs. 0%) increased significantly between the intervention and baseline periods. However, the rates of documentation of abuse did not change.

CONCLUSIONS

This intervention was successful in increasing provider perceived knowledge and comfort; however, comfort decreased at follow-up. Additionally, the rates of screening and referrals increased 6 months post-training. Health care provider training and support and integrated quality assurance mechanisms may be necessary to increase the overall rate of these activities, and to sustain this effort over time. Further study is needed to identify effective methods to increase provider comfort regarding DV screening.

Selective synaptic plasticity within the cerebellar cortex following complex motor skill learning

Complex motor skill learning, but not mere motor activity, leads to an increase in synapse number within the cerebellar cortex. The present experiment used quantitative electron microscopy to determine which synapse types were altered in number. Adult female rats were allocated to either an acrobatic condition (AC), a voluntary exercise condition (VX), or an inactive condition (IC). AC animals were trained to traverse an elevated obstacle course requiring substantial motor coordination to complete. VX animals were housed with unlimited access to running wheels and IC animals received no motor training but were handled briefly each day. Results showed the AC animals to have significantly more parallel fiber to Purkinje cell synapses than both the VX and IC animals. No other synapse type was significantly altered. Thus, the learning-dependent increase in synapse number observed within the cerebellar cortex is accomplished primarily through the addition of parallel fiber synapses.

SMART START: an option for adolescents to delay the pelvic examination and blood work in family planning clinics

PURPOSE

The goal was to encourage earlier use of family planning services and effective birth control for teens.

METHOD

In three federally-funded family planning clinics, the SMART START service model was offered to non-pregnant teens under 18. Teens making their first family planning visit to the clinics for family planning services had the option to delay the requisite pelvic examination and blood work following a careful medical and social history for up to 6 months while obtaining oral contraceptives and/or other non-prescriptive contraceptives. Each teen also received individualized counseling and follow-up telephone contacts. Survey and medical chart data were collected during the project period to evaluate the effects of SMART START on 151 teens.

RESULTS

Of the 151 teens, 26% delayed the pelvic examination and 40% delayed the blood work. The delay of medical services did not result in negative health outcomes. Teens who elected to delay the pelvic examination returned to the clinic as frequently for revisits, they reported using condoms more consistently, they had fewer pregnancies and had similar STD rates compared with those not delaying. SMART START also found that ethnic factors correlated with deferring the blood work.

CONCLUSIONS

SMART START offered teens options over how and when they receive reproductive health care services without withholding effective contraceptive methods. No serious complications of STDs resulted from the delay procedures. Expansion of the SMART START model to include both teen and adult populations is encouraged.

Autoregulation of 2 micron circle gene expression provides a model for maintenance of stable plasmid copy levels

The yeast plasmid 2 micron circle actively maintains high but stable copy levels in the cell, even though the plasmid confers no selective advantage to its host. To address the mechanism by which stable copy control is achieved, we have examined the level of expression of the genes resident on the yeast plasmid 2 micron circle as a function of the presence of proteins encoded by the plasmid. We find that transcription of the site-specific recombinase gene, FLP, is repressed at least 100-fold by the concerted action of the products of two other plasmid genes, REP1 and REP2. In addition, these products repress transcription of the REP1 gene itself. These results can be formulated into a consistent model for plasmid copy control.

Characterization of the gene products produced in minicells by pSM1, a derivative of R100

At least ten polypeptides larger than 6 kilodaltons (K) are produced in minicells from the miniplasmid pSM1 in vivo. pSM1 (5804 bp) is a small derivative of the drug resistance plasmid R100 (ca. 90 kb) and carries the R100 essential replication region as well as some non-essential functions. Cloned restriction fragments of pSM1 and plasmids with deletions within pSM1 sequences were used to assign eight of the ten observed polypeptides to specific coding regions of pSM1. Two of these polypeptides were identified as RepA1 and RepA2, proteins encoded by the essential replication region of pSM1/R100. The nucleotide sequence consisting of 885 bp outside the essential replication region is presented here. This sequence contains an open reading frame, orf4, for a protein 22.9 K in size, and one of the pSM1-encoded polypeptides was identified as the orf4 gene product. Five additional polypeptides were shown to be the products of other open reading frames mapping outside the essential replication region. Specific functions have been assigned to four of these polypeptides and tentatively to the fifth.

A 37 X 10(3) molecular weight plasmid-encoded protein is required for replication and copy number control in the plasmid pSC101 and its temperature-sensitive derivative pHS1

Nucleotide sequences were determined for a region essential for autonomous replication and partitioning of pSC101, a plasmid whose replication is dependent on the Escherichia coli dnaA gene product. The essential replication region contains one long coding sequence, rep101 , for a protein composed of 316 amino acids, and a polypeptide approximately 37 X 10(3) Mr in size was identified as the rep101 gene product. rep101 is preceded by two inverted repeat sequences, three directly repeated sequences and a region of high A + T content containing a sequence similar to the E. coli oriC consensus sequence. Because the lesions in seven replication-deficient insertion mutants, four mutants with increased copy number and one temperature-sensitive replication mutant occur within rep101 , the rep101 gene product must control pSC101 replication and copy number. par, a region adjacent to the replication region, which functions in stable plasmid inheritance, contains several inverted repeat sequences.

Site-dependent cleavage of pBR322 DNA by restriction endonuclease HinfI

Cleavage of pBR322 DNA I by the restriction endonuclease HinfI is preferentially inhibited at specific HinfI cleavage sites. These sites in pBR322 DNA I have been identified and ordered with respect to the frequency with which they are cleaved. The HinfI site most resistant to cleavage in pBR322 DNA I is unique in that runs of G-C base pairs are immediately adjacent on both sites. Two differently permuted linear (DNA III) species were produced by cleavage with two different restriction endonucleases, PstI and AvaI. Only one of these linear molecules, that produced by PstI, exhibits the same preferential cleavage pattern as DNA I. The second linear species, that arising from AvaI digestion, shows pronounced relative inhibition of cleavage at the HinfI sites nearest the ends of the molecule (100 to 120 base pairs away, respectively). This result suggest that proximity to the termini of a linear DNA molecule might also influence preferential cleavage. The possibility of formation of stem-loop structures does not appear to influence preferential cleavage by HinfI.

Gene cloning and containment properties of plasmid Col E1 and its derivatives

Colicinogenic plasmid E1 (Col E1) and Col E1 derivatives offer advantages as plasmid cloning vehicles with regard to both utility and biological containment. The Col E1 derivative pCR1 does not alter those essential characteristics of the enfeebled Escherichia coli strain x1776 that make this strain particularly useful as a host-vehicle system for recombinant DNA research.

Method for the isolation of Escherichia coli K-12 mutants deficient in essential genes

We developed a general procedure for the induction and identification of mutations in chromosomal essential genes that are located in a diploid region of Escherichia coli K-12. The partial diploidy is conferred by an episome that is temperature sensitive for replication so that a mutant strain will form microcolonies at 42 C on complete media if an essential chromosomal gene in the diploid region is defective. Mutations identified by this procedure can be classified into cistrons by a complementation method devised for the purpose. To verify that the procedure works in practice, we fused an episome covering the rif region with an Ftslac+ and used the resulting temperature-sensitive episome to identify chromosomal mutations in essential functions near rif. As expected, a certain proportion of the mutations were in the rif gene, an essential gene that codes for the beta subunit of ribonucleic acid polymerase.

Essential genes in the metB-malB region of Escherichia coli K-12

We isolated 25 independent mutants that are deficient in essential genes located in the metB-malB region of the Escherichia coli chromosome. The mutations were mapped within this region by using several F' factors and were also classified into 11 cistrons by complementation testing. There is clustering of mutations in essential genes within the metB-malB region.