Change in surface characteristics and permeability of human enamel after subjecting to radiation therapy

BACKGROUND

Radiation-related caries is a complex destructive lesion leading to uncompromising damage of enamel and dentin in patients suffering from head and neck cancer managed with radiotherapy.

AIM

The purpose of this study was to evaluate the changes in the permeability of enamel and to assess the morphological and chemical changes of teeth surface subjected to 6 MV photon beam irradiation.

MATERIALS AND METHODS

For this in vitro study, coronal portion of 20 premolars were sectioned mesiodistally into halves and then grouped into two. Samples in group 1 (control) were not subjected to cycles of irradiation and those in group 2 (experimental) were subjected to a cumulative uniform radiation dose of 70 Gray fractioned in 35 fractions with 6 MV photons. The silver nitrate penetration method was used to assess the change in permeability of enamel. The variations in surface topography and mineral content were assessed using scanning electron microscopy with energy dispersive X-ray analysis. Dye penetration scores of surface texture changes were compared between the two groups utilizing the Chi-square test. The change in the elemental levels between enamel surfaces of the two groups was compared using an independent t-test.

RESULTS

The application of 6 MV photon radiation did not change enamel permeability and surface topography. However, a noteworthy reduction in the carbon content (P = 0.002) was observed in teeth subjected to irradiation.

CONCLUSIONS

Though radiation exposure did not alter the enamel permeability and surface topography, it had caused significant chemical compositional changes. Carbon content was significantly reduced in irradiated enamel samples.

Ileal Perforation and Enteric Fever: Implications for Burden of Disease Estimation

Background

Ileal perforation occurs in about 1% of enteric fevers as a complication, with a case fatality risk (CFR) of 20%–30% in the early 1990s that decreased to 15.4% in 2011 in South East Asia. We report nontraumatic ileal perforations and its associated CFR from a 2-year prospective enteric fever surveillance across India.

Methods

The Surveillance for Enteric Fever in India (SEFI) project established a multitiered surveillance system for enteric fever between December 2017 and March 2020. Nontraumatic ileal perforations were surveilled at 8 tertiary care and 6 secondary care hospitals and classified according to etiology.

Results

Of the 158 nontraumatic ileal perforation cases identified,126 were consented and enrolled. Enteric fever (34.7%), tuberculosis (19.0%), malignancy (5.8%), and perforation of Meckel diverticulum (4.9%) were the common etiology. In those with enteric fever ileal perforation, the CFR was 7.1%.

Conclusions

Enteric fever remains the most common cause of nontraumatic ileal perforation in India, followed by tuberculosis. Better modalities of establishing etiology are required to classify the illness, and frame management guidelines and preventive measures. CFR data are critical for comprehensive disease burden estimation and policymaking.

Cost of Illness Due to Severe Enteric Fever in India

Background

Lack of robust data on economic burden due to enteric fever in India has made decision making on typhoid vaccination a challenge. Surveillance for Enteric Fever network was established to address gaps in typhoid disease and economic burden.

Methods

Patients hospitalized with blood culture-confirmed enteric fever and nontraumatic ileal perforation were identified at 14 hospitals. These sites represent urban referral hospitals (tier 3) and smaller hospitals in urban slums, remote rural, and tribal settings (tier 2). Cost of illness and productivity loss data from onset to 28 days after discharge from hospital were collected using a structured questionnaire. The direct and indirect costs of an illness episode were analyzed by type of setting.

Results

In total, 274 patients from tier 2 surveillance, 891 patients from tier 3 surveillance, and 110 ileal perforation patients provided the cost of illness data. The mean direct cost of severe enteric fever was US$119.1 (95% confidence interval [CI], US$85.8–152.4) in tier 2 and US$405.7 (95% CI, 366.9–444.4) in tier 3; 16.9% of patients in tier 3 experienced catastrophic expenditure.

Conclusions

The cost of treating enteric fever is considerable and likely to increase with emerging antimicrobial resistance. Equitable preventive strategies are urgently needed.

Optimizing MRI of small joints and extremities

Obtaining optimal images of small joints using magnetic resonance imaging (MRI) can be technically challenging. The aim of this review is to outline the practical aspects of MRI of small joints, with reference to the underlying physical principles. Although the most important contribution to successful imaging of small joints comes from the magnet field strength and design of the receiver coil, there are a number of factors to balance including the signal-to-noise ratio, image resolution, and acquisition times. We discuss strategies to minimize artefacts from movement, inhomogeneity, chemical shift, and fat suppression. As with all MRI, each strategy comes at a price, but the benefits and costs of each approach can be fine-tuned to each combination of joint, receiver coil, and MRI machine.

Tumour-to-tumour metastasis of laryngeal leiomyosarcoma to an axillary hibernoma

Tumour-to-tumour metastasis is a rare, but well-recognised occurrence. This case report documents the metastasis of a primary laryngeal leiomyosarcoma to a hibernoma. We believe that this is the first recorded case of leiomyosarcoma metastasising to another neoplasm, and the first recorded case of a hibernoma acting as a recipient tumour for metastasis. This case study emphasises the importance of re-imaging a known benign mass in the presence of new symptoms in a patient with underlying malignancy, to ensure prompt diagnosis and management of potentially treatable metastasis. The imaging findings including whole body magnetic resonance imaging (MRI) staging, macroscopic and histological features are presented.

Profunda femoris pseudoaneurysm following Birmingham hip resurfacing: an important differential diagnosis for a periarticular cystic mass

Vascular injury following hip resurfacing arthroplasty is rare: we present a case of profunda femoris pseudoaneurysm complicating hip resurfacing arthroplasty performed via an anterolateral approach. Over recent years, it has been recognized that an adverse reaction to metal debris from metal-on-metal arthroplasties can also result in the development of cystic masses around the hip. This case highlights a potential rare differential diagnosis that needs to be considered when imaging cystic mass lesions around the postoperative hip. Imaging can provide a definitive diagnosis if this entity is considered and its appearances recognized, resulting in appropriate management of this potentially limb- and life-threatening complication.

Asthma and oral health: a review

Asthma is a chronic inflammatory condition that causes the airways to constrict and produce excess mucus, making breathing difficult. It is characterized by the obstruction of airflow which is variable over a short period of time. This condition is reversible, either spontaneously or can be controlled with the help of drugs. Asthma medication comprises bronchodilators, corticosteroids and anticholinergic drugs. Most of these drugs are inhaled using various forms of inhalers or nebulizers. The effect of these drugs on oral health is the subject of debate among dental practitioners. Patients taking asthma medication may be at risk of dental caries, dental erosion, periodontal diseases and oral candidiasis. Hence, patients with bronchial asthma on medication should receive special prophylactic attention. This article reviews the correlation between asthma and oral health, and suggests various measures to counter possible oral health problems related to asthma.

Three rooted, four canalled mandibular first molar (Radix Entomolaris)

A mandibular first molar with two distal roots is an interesting example of anatomic variation. This paper describes case reports of mandibular first molar with three roots (one mesial and two distal) and four canals (two in mesial and one in each distobuccal and distolingual root). The canals were shaped with protaper rotary files and irrigated with 5.25% sodium hyochlorite, 0.2 %w/v of chlorhexidine gluconate and normal saline as the fi nal irrigant. The canals were then obturated with gutta- percha and AH plus sealer. These case reports show an anatomic variation of internal morphology of the tooth and points out the importance of searching for additional canals.

Immunization with an interferon-gamma-gp120 fusion protein induces enhanced immune responses to human immunodeficiency virus gp120

Cytokines, including interferon (IFN)-gamma, can be effective immunologic adjuvants but often lack the potency of other, more reactogenic compounds. On the basis of the observation that attachment of IFN-gamma to antigen could further enhance its adjuvanticity, a chimeric protein involving IFN-gamma and gp120 of human immunodeficiency virus was produced, using varying lengths of amino acid linkers between the two moieties. All resultant fusion proteins appeared to be dimerized, but full IFN-gamma biological activity was present only with the longest, 34-aa linker. Immunization with the fusion protein gave rise to enhanced primary antibody responses to gp120, particularly of the IgG2a subclass. In addition, both T cell proliferation and IFN-gamma production in response to antigen were strongly enhanced by primary immunization with the fusion protein. IFN-gamma fused to antigen is a more potent adjuvant for Th1-like responses than is IFN-gamma mixed with antigen.

UP element-dependent transcription at the Escherichia coli rrnB P1 promoter: positional requirements and role of the RNA polymerase alpha subunit linker

The UP element stimulates transcription from the rrnB P1 promoter through a direct interaction with the C-terminal domain of the RNA polymerase alpha subunit (alphaCTD). We investigated the effect on transcription from rrnB P1 of varying both the location of the UP element and the length of the alpha subunit interdomain linker, separately and in combination. Displacement of the UP element by a single turn of the DNA helix resulted in a large decrease in transcription from rrnB P1, while displacement by half a turn or two turns totally abolished UP element-dependent transcription. Deletions of six or more amino acids from within the alpha subunit linker resulted in a decrease in UP element-dependent stimulation, which correlated with decreased binding of alphaCTD to the UP element. Increasing the alpha linker length was less deleterious to RNA polymerase function at rrnB P1 but did not compensate for the decrease in activation that resulted from displacing the UP element. Our results suggest that the location of the UP element at rrnB P1 is crucial to its function and that the natural length of the alpha subunit linker is optimal for utilisation of the UP element at this promoter.

Assessment of coronary arterial restenosis with phase-contrast magnetic resonance imaging measurements of coronary flow reserve

BACKGROUND

After successful percutaneous coronary arterial revascularization, 25% to 60% of subjects have restenosis, a recurrent coronary arterial narrowing at the site of the intervention. At present, restenosis is usually detected invasively with contrast coronary angiography. This study was performed to determine if phase-contrast MRI (PC-MRI) could be used to detect restenosis noninvasively in patients with recurrent chest pain after percutaneous revascularization.

METHODS AND RESULTS

Seventeen patients (15 men, 2 women, age 36 to 77 years) with recurrent chest pain >3 months after successful percutaneous intervention underwent PC-MRI measurements of coronary artery flow reserve followed by assessments of stenosis severity with computer-assisted quantitative coronary angiography. The intervention was performed in the left anterior descending coronary artery in 15 patients, one of its diagonal branches in 2 patients, and the right coronary artery in 1 patient. A PC-MRI coronary flow reserve value </=2.0 was 100% and 82% sensitive and 89% and 100% specific for detecting a luminal diameter narrowing of >/=70% and >/=50%, respectively.

CONCLUSIONS

Assessments of coronary flow reserve with PC-MRI can be used to identify flow-limiting stenoses (luminal diameter narrowings >70%) in patients with recurrent chest pain in the months after a successful percutaneous intervention.

The Escherichia coli RNA polymerase alpha subunit linker: length requirements for transcription activation at CRP-dependent promoters

The C-terminal domain of the Escherichia coli RNA polymerase alpha subunit (alphaCTD) plays a key role in transcription initiation at many activator-dependent promoters. This domain is connected to the N-terminal domain by an unstructured linker, which is proposed to confer a high degree of mobility on alphaCTD. To investigate the role of this linker in transcription activation we tested the effect of altering the linker length on promoters dependent on the cyclic AMP receptor protein (CRP). Short deletions within the alpha linker decrease CRP-dependent transcription at a Class I promoter while increasing the activity of a Class II promoter. Linker extension impairs CRP-dependent transcription from both promoters, with short extensions exerting a more marked effect on the Class II promoter. Activation at both classes of promoter was shown to remain dependent upon activating region 1 of CRP. These results show that the response to CRP of RNA polymerase containing linker-modified alpha subunits is class specific. These observations have important implications for the architecture of transcription initiation complexes at CRP-dependent promoters.

Transcription activation at the Escherichia coli melAB promoter: the role of MelR and the cyclic AMP receptor protein

MelR is a melibiose-triggered transcription activator that belongs to the AraC family of transcription factors. Using purified Escherichia coli RNA polymerase and a cloned DNA fragment carrying the entire melibiose operon intergenic region, we have demonstrated in vitro open complex formation and activation of transcription initiation at the melAB promoter. This activation is dependent on MelR and melibiose. These studies also show that the cyclic AMP receptor protein (CRP) interacts with the melAB promoter and increases MelR-dependent transcription activation. DNAase I footprinting has been exploited to investigate the location of MelR-and CRP-binding sites at the melAB promoter. We showed previously that MelR binds to two identical 18 bp target sequences centred at position -100.5 (Site 1) and position -62.5 (Site 2). In this work, we show that MelR additionally binds to two other related 18 bp sequences: Site 1', centred at position -120.5, located immediately upstream of Site 1, and Site R, at position -238.5, which overlaps the transcription start site of the divergent melR promoter. MelR can bind to Site 1', Site 1, Site 2 and Site R, in both the absence and the presence of melibiose. However, in the presence of melibiose, MelR also binds to a fifth site (Site 2', centred at position -42.5) located immediately downstream of Site 2, and overlapping the -35 region of the melAB promoter. Additionally, although CRP is unable to bind to the melAB promoter in the absence of MelR, in the presence of MelR, it binds to a site located between MelR binding Site 1 and Site 2. Thus, tandem-bound MelR recruits CRP to the MelR. We propose that expression from the melAB promoter has an absolute requirement for MelR binding to Site 2'. Optimal expression of the melAB promoter requires Sites 1', Site 1, Site 2 and Site 2'; CRP acts as a 'bridge' between MelR bound at Sites 1' and 1 and at Sites 2 and 2', increasing expression from the melAB promoter. In support of this model, we show that improvement of the base sequence of Site 2' removes the requirement for Site 1' and Site 1, and short circuits the effects of CRP.

Utility of fast cine magnetic resonance imaging and display for the detection of myocardial ischemia in patients not well suited for second harmonic stress echocardiography

BACKGROUND

Some patients referred for pharmacological stress testing with transthoracic echocardiography (TTE) are unable to undergo testing owing to poor acoustic windows. Fast cine MRI can be used to assess left ventricular contraction, but its utility for detection of myocardial ischemia in patients poorly suited for echocardiography is unknown.

METHODS AND RESULTS

One hundred fifty-three patients (86 men and 67 women aged 30 to 88 years) with poor acoustic windows that prevented adequate second harmonic TTE imaging were consecutively referred for MRI to diagnose inducible myocardial ischemia during intravenous dobutamine and atropine. Diagnostic studies were completed in an average of 53 minutes. No patients experienced myocardial infarction, ventricular fibrillation, exacerbation of congestive heart failure, or death. In patients who underwent computer-assisted quantitative coronary angiography, the sensitivity and specificity for detecting a >50% luminal diameter narrowing were 83% and 83%, respectively. In the 103 patients with a negative MRI examination, the cardiovascular occurrence-free survival rate was 97%.

CONCLUSIONS

Fast cine cardiac MRI provides a mechanism to assess left ventricular contraction and diagnose inducible myocardial ischemia in patients not well suited for stress echocardiography.

Cell surface expression of CD154 inhibits alloantibody responses: A mechanism for the prevention of autoimmune responses against activated T cells?

Binding of CD40 by CD154 expressed on activated T cells is a pivotal event in T cell help to B cells, macrophages, and other antigen-presenting cells. Expression of CD154 by MHC mismatched cells, in contrast to expectations, strongly suppressed alloantibody responses against the cells. This was caused by a failure of priming of antibody responses by the CD154 expressing cells. We hypothesize that this lack of response against CD154 expressing cells may represent a mechanism that has evolved to prevent autoantibody responses being generated against the CD154 antigen itself, as B cells expressing antibody reactive with CD154 would probably escape deletion on binding antigen in the bone marrow due to rescue by the simultaneous ligation of CD40.

Visualization and functional assessment of proximal and middle left anterior descending coronary stenoses in humans with magnetic resonance imaging

BACKGROUND

Coronary artery bypass grafting improves survival in patients with >70% luminal diameter narrowing of the 3 major epicardial coronary arteries, particularly if there is involvement of the proximal portion of the left anterior descending (LAD) coronary artery. Measurement of coronary flow reserve can be used to identify functionally important luminal narrowing of the LAD artery. Although magnetic resonance imaging (MRI) has been used to visualize coronary arteries and to measure flow reserve noninvasively, the utility of MRI for detecting significant LAD stenoses is unknown.

METHODS AND RESULTS

Thirty subjects (23 men, 7 women, age 36 to 77 years) underwent MRI visualization of the left main and LAD coronary arteries as well as measurement of flow in the proximal, middle, or distal LAD both at rest and after intravenous adenosine (140 microgram/kg per minute). Immediately thereafter, contrast coronary angiography and when feasible, intracoronary Doppler assessments of coronary flow reserve, were performed. There was a statistically significant correlation between MRI assessments of coronary flow reserve and (a) assessments of coronary arterial stenosis severity by quantitative coronary angiography and (b) invasive measurements of coronary flow reserve (P<0.0001 for both). In comparison to computer-assisted quantitative coronary angiography, the sensitivity and specificity of MRI for identifying a stenosis >70% in the distal left main or proximal/middle LAD arteries was 100% and 83%, respectively.

CONCLUSIONS

Noninvasive MRI measures of coronary flow reserve correlated well with similar measures obtained with the use of intracoronary Doppler flow wires and predicted significant coronary stenoses (>70%) with a high degree of sensitivity and specificity. MRI-based measurement of coronary flow reserve may prove useful for identification of patients likely to obtain a survival benefit from coronary artery bypass grafting.

Rethinking specialist integration strategies

To surmount the economic pressures of managed care, specialists are pursuing various initiatives designed to increase revenues and market share that may put them into competition with healthcare systems. Systems contemplating collaboration with specialists to gain their loyalty may first consider employing a strategy involving physician gain sharing. It should be understood, however, that there are legal hurdles to be overcome in developing gain sharing, that there are different gain-sharing models to be used, and that there are limitations as well as benefits to such an initiative. These limitations require healthcare systems to consider other, more durable specialist integration strategies. The balance of power between a healthcare system and specialists will affect the success of whatever integration strategy is employed.

The Escherichia coli RNA polymerase alpha subunit and transcriptional activation by bacteriophage lambda CII protein

Bacteriophage lambda is not able to lysogenise the Escherichia coli rpoA341 mutant. This mutation causes a single amino acid substitution Lys271Glu in the C-terminal domain of the RNA polymerase alpha subunit (alphaCTD). Our previous studies indicated that the impaired lysogenisation of the rpoA341 host is due to a defect in transcriptional activation by the phage CII protein and suggested a role for alphaCTD in this process. Here we used a series of truncation and point mutants in the rpoA gene placed on a plasmid to investigate the process of transcriptional activation by the cII gene product. Our results indicate that amino-acid residues 265, 268 and 271 in the a subunit may play an important role in the CII-mediated activation of the pE promoter (most probably residue 271) or may be involved in putative interactions between alphaCTD and an UP-like element near pE (most probably residues 265 and 268). Measurement of the activity of pE-lacZ, pI-lacZ and p(aQ)-lacZ fusions in the rpoA+ and rpoA341 hosts demonstrated that the mechanism of activation of these CII-dependent promoters may be in each case different.

The Escherichia coli RNA polymerase alpha subunit and transcriptional activation by bacteriophage lambda CII protein

Bacteriophage lambda is not able to lysogenise the Escherichia coli rpoA341 mutant. This mutation causes a single amino acid substitution Lys271Glu in the C-terminal domain of the RNA polymerase alpha subunit (alphaCTD). Our previous studies indicated that the impaired lysogenisation of the rpoA341 host is due to a defect in transcriptional activation by the phage CII protein and suggested a role for alphaCTD in this process. Here we used a series of truncation and point mutants in the rpoA gene placed on a plasmid to investigate the process of transcriptional activation by the cII gene product. Our results indicate that amino-acid residues 265, 268 and 271 in the a subunit may play an important role in the CII-mediated activation of the pE promoter (most probably residue 271) or may be involved in putative interactions between alphaCTD and an UP-like element near pE (most probably residues 265 and 268). Measurement of the activity of pE-lacZ, pI-lacZ and p(aQ)-lacZ fusions in the rpoA+ and rpoA341 hosts demonstrated that the mechanism of activation of these CII-dependent promoters may be in each case different.

The effect of a nested set of C-terminal substituted deletions on the function of the alpha subunit of Escherichia coli RNA polymerase

A genetic screen was devised to obtain plasmid-borne rpoA alleles exhibiting partial or no complementation of the chromosomal Escherichia coli rpoA341 allele responsible for a pleiotropic phenotype. Nine of the ten mutants obtained carried single base pair deletions within the 3' end of rpoA resulting in frameshifting into a 72 codon +1 orf extending from within codon L262 and terminating 16 bp downstream of the rpoA reading frame. These frameshifts give rise to a set of substituted alpha deletions that are all of the same size (334 aa) and carry segments of the Orf sequence replacing the alpha region from the C-terminus (residue 329) to various points between 272 > 319. The in vivo properties of this nested set of nine C-terminal-substituted derivatives of the alpha subunit of RNA polymerase have been assessed in terms of their assembly and transcriptional proficiency. The results indicate: (i) replacement of as much as 42 C-terminal residues of the alpha subunit does not prevent formation of a transcriptionally proficient holoenzyme form of RNA polymerase capable of complementing rpoA112(Ts); (ii) the extreme C-terminal Orf region, like that of alpha itself, is exposed in holoenzyme; (iii) these substituted deletions are not commonly functional at class I activated promoters.

The future of physician practice management companies

Physician practice management (PPM) companies are growing sector of the healthcare industry and have caught the attention of Wall Street, as evidenced by the number of initial public offerings of PPMs in the past three years. The cost of operating efficiencies, declining premiums, integration, oversupply of specialists, shift from a gatekeeper to a direct-access model, and cultural challenges are the emerging market forces that may affect PPM viability. The challenge for PPMs is to maintain earnings growth in the face of these market forces.

DNA binding and DNA bending by the MelR transcription activator protein from Escherichia coli

The Escherichia coli melR gene encodes MelR protein which is a member of the AraC/XylS family of bacterial transcription activators. The function of MelR was investigated by making a targeted deletion in the melR gene of the Escherichia coli chromosome. MelR is a transcription activator essential for melibiose- dependent expression of the melAB operon which is needed for bacterial growth with melibiose as a carbon source. To investigate the interactions of MelR at the melAB promoter, both full length MelR and a shortened derivative, MelR173, containing the C-terminal DNA-binding domain, were purified as fusions to glutathione- S -transferase. Circular permutation studies show that both full-length MelR and MelR173 induce an apparent bend upon binding to target sites at the melAB promoter. Bound full-length MelR, but not MelR173, can oligomerise to form larger complexes that are likely to be involved in transcription activation.

Impaired lysogenisation of the Escherichia coli rpoA341 mutant by bacteriophage lambda is due to the inability of CII to act as a transcriptional activator

The C-terminus of the alpha subunit of Escherichia coli RNA polymerase is known to function in transcriptional activation at certain promoters. This region was previously shown to be necessary for full activation of the pE promoter by the phage lambda CII protein in vitro. In this work we investigated the inability of phage lambda to follow the lysogenic pathway in cells carrying the point mutation rpoA341 (a change of lysine 271 to glutamic acid). We found that neither overexpression of the cII gene nor stabilisation of the CII protein by the can1 mutation or by cIII gene overexpression was able to suppress the block in lysogenisation. In contrast, the lambda cin1 phage, which carries a CII-independent promoter for the expression of the cI gene, was able to efficiently lysogenise the rpoA341 mutant strain. Furthermore, the rpoA341 mutation prevented the activation of pE-lacZ and pI-lacZ transcriptional fusions by CII. Therefore we conclude that transcriptional activation by the cII gene product is abolished by the rpoA341 mutation, most probably due to impaired interaction between the CII activator and mutant RNA polymerase. The inability of RNA polymerase to respond to CII results in the impairment of lysogenisation of the rpoA341 mutant by phage lambda.

An RNA polymerase alpha subunit mutant impairs N-dependent transcriptional antitermination in Escherichia coli

We show that the rpoA341 mutation in the gene encoding the alpha subunit of Escherichia coli RNA polymerase results in a decreased level of transcripts originating from the lytic promoters PL and PR of infecting lambda phage. However, using lacZ fusions we demonstrate that initiation of transcription from both PL and PR is not impaired in the rpoA341 host. Rather, it is the level of the longer, antiterminated PL- and PR-derived transcripts which is altered: the activity of beta-galactosidase in bacteria harbouring a source of N and a PL-nutL-tL1-tI-lacZ or PR-nutR-tR1-lacZ fusion is considerably lower in the rpoA341 mutant relative to the rpoA+ strain. In the absence of the antiterminator protein N no difference is observed in the level of longer PR-derived transcripts between wild-type (rpoA+) and mutant (rpoA341) hosts. Although synthesis of N appears to be similar in both phage-infected rpoA+ and rpoA341 cells, overexpression of the N gene leads to restoration of wild-type levels of the longer PL- and PR-derived transcripts in the mutant host. While this mutation does not appear to affect vegetative phage growth in nus+ backgrounds, in combination with certain nus mutations it retards lytic development. Therefore, we conclude that the rpoA341 mutation specifically interferes with the function of the N-antitermination complex, suggesting that the C-terminal domain of the RNA polymerase alpha subunit may play an important role in N-dependent transcriptional antitermination.

A nested set of C-terminal deletions of the alpha subunit of Escherichia coli RNA polymerase define regions concerned with assembly, proteolysis, stabilization and transcriptional activation in vivo

BACKGROUND

The alpha subunit of eubacterial RNA polymerase comprises an N-terminal assembly domain and a mobile C-terminal domain which provides an activation contact site for class I transcription activators. One particular C-terminal alpha mutant, rpoA341, impairs the response of Escherichia coli RNA polymerase to several activators, including MelR.

RESULTS

The in vivo properties of a set of C-terminally truncated alpha variants were investigated. Derivatives of 230 amino acids or longer were assembled into functional RNA polymerase. However, derivatives greater than 271 residues in length were sensitised to proteolysis near K271. Deletion of only 13 C-terminal amino acids impaired the response to CRP at a class I promoter whereas the complete removal of the alpha C-terminal domain did not prevent complementation of MelR-dependent PmelAB activity in the rpoA341 mutant.

CONCLUSIONS

Our results refine the C-terminal limit of the alpha assembly domain to between residues 221 and 230. The 13 extreme C-terminal amino acids are exposed in the holoenzyme and participate in the protection of an otherwise proteolytically sensitive bond near K271. Their presence is also essential for transcription activation at class I CRP-dependent promoters. The rpoA341-mediated substitution, K271E, does not define an activation contact site for MelR.

Drastically decreased transcription from CII-activated promoters is responsible for impaired lysogenization of the Escherichia coli rpoA341 mutant by bacteriophage lambda

It was demonstrated previously that a mutation, rpoA341, in the gene encoding the alpha subunit of Escherichia coli RNA polymerase prevents lysogenization by bacteriophage lambda. The rpoA341 allele is known to be responsible for impaired transcription of some positively regulated E. coli chromosomal operons. Here we demonstrate that the inhibition of lysogenization of the rpoA341 mutant is a result of drastically decreased transcription from positively regulated phage promoters. We were unable to detect any transcripts originating from the CII-activated pE, pI and paQ promoters (important for lysogenic development) in the phage-infected rpoA341 mutant, in contrast to an otherwise isogenic rpoA+ strain. The results are discussed in the light of other reports showing that activation of the pE promoter by CII protein in vitro is decreased only about fivefold when the native alpha subunit is replaced by truncated alpha polypeptides.

Retention of low copy number human papillomavirus DNA in cultured cutaneous and mucosal wart keratinocytes

Cultured wart keratinocytes have previously been described as having a limited proclivity to maintain episomal human papillomavirus (HPV) DNA. To investigate the nature of episome loss, and to determine keratinocyte-specific factors involved in it, we have examined a large series of anogenital and oral wart keratinocyte cultures, tracing episomal copy number with culture passage. We report that a higher proportion of oral wart keratinocytes maintain episomal HPV DNA to first passage (70% compared with 37% of anogenital wart cultures) when screened by slot blot hybridization. Furthermore, oral wart keratinocytes maintain episomal HPV copy through a greater number of passages (60% positive at passage 2 compared with 2% of anogenital wart cultures) with this technique. When anogenital cultures were examined at first passage for HPV infection by PCR with Southern blot hybridization of the product, a further 34% were found to be HPV-positive. To determine the mechanism of loss of episomal DNA from these cultures we examined the relative HPV copy number in cells which adhered to the culture vessel following passage and in those which did not adhere. Those which remained floating contained episomal HPV at high copy number whereas those which adhered were negative by slot blotting. The adherent cells, however, remained positive by PCR at subsequent passages until senescence. We conclude that a subpopulation of HPV-positive keratinocytes may be maintained in culture through serial passage until senescence.

Involvement of the Escherichia coli RNA polymerase alpha subunit in transcriptional activation by the bacteriophage lambda CI and CII proteins

Escherichia coli cells harbouring the rpoA341 mutation produce an RNA polymerase which transcribes inefficiently certain operons subject to positive control. Here, we demonstrate that the rpoA341 allele also prevents lysogenization of the host strain by bacteriophage lambda, a process dependent upon the action of two phage-encoded activators. This phenomenon was shown to arise from an inability to establish an integrated prophage rather than a failure to maintain the lysogenic state. The inability of the rpoA341 host to support lysogenization could be completely reversed by CII-independent expression of int and cI in trans. These results led us to propose that the inhibition of lysogenization arises from a defective interaction between the phage lambda transcriptional activator CII and the mutant RNA polymerase at the phage promoters pI and pE. Finally, we also provide genetic evidence for impaired transcription of the cI gene from the CI-activated promoter, pM in the rpoA341 background.

Acute renal failure secondary to myoglobinuria

Acute Renal Failure (ARF) secondary to rhabdomyolysis and myoglobinuria was seen in four patients. In three, this was secondary to trauma and the fourth patient had an inflammatory myositis. All 4 patients had total recovery of renal function.

Type II paralysis or intermediate syndrome following organophosphorous poisoning

Three cases of type II paralysis or intermediate syndrome following organophosphorous poisoning are reported. Two patients had an initial improvement followed by development of paralysis of neck flexors, cranial nerves, proximal muscles of the limbs and respiratory muscles, which occurred 48 to 96 hours after the poisoning. All the patients recovered completely.

Association between the herpes simplex virus major DNA-binding protein and alkaline nuclease

Herpes simplex virus encodes seven proteins which have been shown to be both necessary and sufficient for in vitro replication of origin-containing plasmids. We have shown previously that one of these proteins, the major DNA-binding protein mDBP, forms a complex with alkaline nuclease, which is not one of the seven essential proteins. In this study, we have employed immunological reagents and a series of deletion mutants to investigate this complex further. We have determined the regions of mDBP which are important in the formation of this complex, and we have shown that the intranuclear locations of alkaline nuclease and major DNA-binding protein overlap.

Escherichia coli rpoA mutation which impairs transcription of positively regulated systems

The rpoA341 (phs) mutation of Escherichia coli results in decreased expression of several positively regulated operons and has been mapped to within or very near the rpoA gene encoding the alpha subunit of RNA polymerase. We have shown that plasmid-directed synthesis of the wild-type alpha subunit can complement the defective phenotypes associated with this mutation consistent with its proposed location within rpoA. This mutation was mapped by marker rescue to within a 182bp region near the 3' end of rpoA and was subsequently transferred to a plasmid by recombination in vivo. DNA sequence analysis revealed that the RpoA341 phenotype was the result of the substitution of lysine 271 by glutamate within the alpha polypeptide. We discuss this result in relation to our current understanding of the functional organization of the alpha subunit.

High level expression of DNA polymerases from herpesviruses

The DNA polymerase genes of human cytomegalovirus (HCMV) and varicella-zoster virus (VZV) were inserted separately into the polyhedrin gene of Autographa californica nuclear polyhedrosis virus (AcNPV) by cotransfection of Spodoptera frugiperda (SF9) cells with baculovirus transfer vectors carrying the genes and AcNPV infectious DNA. Infection of SF9 cells with the recombinant viruses resulted in expression from the polyhedrin promoter of proteins of the expected Mrs. These proteins possessed DNA polymerase activities similar to that of the enzymes induced by the respective herpesvirus in infected cells, and were identified as HCMV and VZV DNA polymerase using inhibitors and specific antisera reactive with each enzyme.

Identification of an enhancer element for the endosperm-specific expression of high molecular weight glutenin

Genes encoding high molecular weight (HMW) glutenin, a wheat seed storage protein, are expressed only in the developing endosperm. It was previously demonstrated that sequences essential for endosperm-specific transcription reside within 436 base pairs upstream of the initiation codon for HMW glutenin translation. We have further analyzed this region by testing the ability of a series of truncated HMW glutenin promoter fragments to enhance transcription from an adjacent heterologous promoter. The activity of these hybrid promoters was determined by measuring the expression of a linked beta-glucuronidase (GUS) reporter gene in transgenic tobacco plants. An HMW glutenin promoter fragment spanning nucleotides -375 to -45 relative to the transcription start site was found to stimulate GUS expression in tobacco seeds when inserted in either orientation upstream of the heterologous promoter. Furthermore, this fragment could also potentiate transcription when located 3' to the GUS reporter gene. Stimulation of GUS gene expression in transgenic tobacco seeds did not occur until 9 days to 12 days after anthesis, coincident with the onset of storage protein synthesis in the developing tobacco and wheat seed, and was confined to the endosperm tissue. By testing progressively shorter promoter fragments, the enhancer element responsible for this pattern of expression was localized to a 40-base pair region some 170 base pairs upstream of the start site for HMW glutenin transcription.

Identification of an enhancer element for the endosperm-specific expression of high molecular weight glutenin

Genes encoding high molecular weight (HMW) glutenin, a wheat seed storage protein, are expressed only in the developing endosperm. It was previously demonstrated that sequences essential for endosperm-specific transcription reside within 436 base pairs upstream of the initiation codon for HMW glutenin translation. We have further analyzed this region by testing the ability of a series of truncated HMW glutenin promoter fragments to enhance transcription from an adjacent heterologous promoter. The activity of these hybrid promoters was determined by measuring the expression of a linked beta-glucuronidase (GUS) reporter gene in transgenic tobacco plants. An HMW glutenin promoter fragment spanning nucleotides -375 to -45 relative to the transcription start site was found to stimulate GUS expression in tobacco seeds when inserted in either orientation upstream of the heterologous promoter. Furthermore, this fragment could also potentiate transcription when located 3' to the GUS reporter gene. Stimulation of GUS gene expression in transgenic tobacco seeds did not occur until 9 days to 12 days after anthesis, coincident with the onset of storage protein synthesis in the developing tobacco and wheat seed, and was confined to the endosperm tissue. By testing progressively shorter promoter fragments, the enhancer element responsible for this pattern of expression was localized to a 40-base pair region some 170 base pairs upstream of the start site for HMW glutenin transcription.

[Evaluation of medical education at the McMaster University, Canada, based on the case method concept]

Students of three different levels and the chairman of the MD-Program evaluated the educational system of McMaster University, Canada, using the six criteria of the case method as defined by Renschler. This analysis provided a very differentiated evaluation of the McMaster curriculum, demonstrating a systematic progress of learning methods from the second to the last phase. The instrument showed differences in the ratings of the demonstrative lectures between the chairman and the students. Free access to patients and responsibility, gradually growing during the 3-year program, are important features of the educational system. The problem-based system provides a unique integration of acquiring theoretical knowledge in the basic sciences through clinical problem solving which was highly rated in all analysed phases. Ratings given by the interviewed students for evaluation of documented work were lower than expected by the chairman and the authors. The results are discussed in relationship to the McMaster Philosophy and to the conditions of studying medicine in America and in Germany.

Production of antibodies of predetermined specificity against herpes simplex virus DNA polymerase and their use in characterization of the enzyme

Peptides from preselected regions of the herpes simplex virus DNA polymerase were used to generate monospecific antisera to defined regions of the enzyme. The antisera were used to localize the polymerase within the infected cell and to determine the time of synthesis during productive infection. Comparison with a neutralizing polyclonal antiserum was used to show the specificity of the peptide antisera. By using the antisera the stabilities of the DNA polymerase, the alkaline nuclease, and the major DNA-binding protein were determined, and the state of phosphorylation of the DNA polymerase was compared with each of these proteins.

S4-alpha mRNA translation repression complex. I. Thermodynamics of formation

Expression of the four ribosomal proteins from the Escherichia coli alpha operon (S4, S11, S13, and L17) is regulated at the level of translation by the binding of S4 to the alpha mRNA. Using a filter binding assay and alpha mRNA sequences prepared by in-vitro transcription, previous work located the S4 target site within the approximately 100-base leader sequence. We have extended this work to include fragments of the alpha leader with six different 5' end points and four different 3' end points. A core region between bases 23 and 69 (numbering from the first nucleotide of the E. coli transcript) binds S4 with an affinity of approximately 2 microM-1. Regions of weak interactions are located in the 22 nucleotides 5' and the 70 nucleotides 3' to this core; they increase the S4 affinity to approximately 13 microM-1. Studies of S4-alpha mRNA binding under different conditions have revealed the following. (1) Specific and non-specific binding show the same dependence on K+ concentration, with delta log+ K/delta log [K+] approximately 4 in most potassium salts. With KCl and KBr, much weaker salt dependence of specific complex formation is observed suggesting that the protein responds to the correct RNA substrate by binding halide anions. (2) Increasing the MgCl2 concentration between 1 and 4 mM enhances binding by a factor of 4, with no further effects up to 20 mM. About five Mg2+ are taken up by the complex with an average binding constant of approximately 600 M-1 each. Renaturation of the RNA in the presence of MgCl2 is also required to obtain full binding. These effects are seen only with alpha mRNA extending beyond the initiation codon; S4 binding to the alpha leader sequence itself is insensitive to Mg2+. (3) The association kinetics are fast and probably diffusion controlled. (4) Formation of the complex is entirely entropy driven.

Regulation of alpha operon gene expression in Escherichia coli. A novel form of translational coupling

The alpha operon of Escherichia coli contains the genes for ribosomal proteins S13, S11, S4, RNA polymerase subunit alpha, and r-protein L17, in this order. Previous studies have shown that translation of all four ribosomal proteins is regulated by S4, and that binding of S4 to the mRNA at the start site for S13 translation is probably responsible for the regulation of translation of S13, S11 and S4. The alpha gene is "unique" in that it is located between the genes for two ribosomal proteins (S4 and L17) and yet appears to be regulated independently of them. In the present studies, we have measured the synthesis rates of all the alpha operon proteins under a variety of physiological conditions. Our results confirm that alpha gene expression is regulated independently of the co-transcribed ribosomal protein genes and is relatively insensitive to translational feedback repression by S4. S1 nuclease analysis of alpha operon mRNA failed to reveal the presence of any unique transcription start or mRNA cleavage that leads to separation of the alpha cistron from preceding ribosomal protein cistrons. Therefore, it appears that differential regulation of alpha synthesis takes place at the level of mRNA translation. We have also carried out a deletion analysis of the alpha operon leader and identified a region of the alpha operon leader mRNA that is required for regulation by S4. Furthermore, deletion of this region results in increased synthesis of L17 together with S13, S11 and S4, whereas alpha synthesis did not increase significantly. Therefore, we conclude that interaction of S4 with this single target site results in translational repression of not only the proximal three cistrons for S13, S11 and S4 but also that of the last cistron, L17, without affecting the intervening alpha cistron.

Intravascular metabolism of lipoprotein cholesteryl esters in African green monkeys: differential fate of doubly labeled cholesteryl oleate

High density lipoproteins (HDL), doubly labeled with [3H]cholesteryl oleate and cholesteryl [14C]oleate, were reinjected to study HDL cholesteryl ester metabolism in African green monkeys. The transfer of labeled HDL cholesteryl ester to low density lipoprotein (LDL) was rapid and equilibration of the [3H]cholesteryl oleate and cholesteryl [14C]oleate specific activities in LDL and HDL occurred within 90 min after reinjection. The apparent rates of disappearance from the circulation of the two moieties of the cholesteryl ester were different. In the same four animals, the residence time for the turnover of plasma [3H]cholesterol averaged 6.1 days while the residence time for the removal of cholesteryl [14C]oleate from plasma was approximately 2.1 days. These results suggest that for some lipoprotein cholesteryl esters removed from plasma, the cholesterol moiety subsequently reappeared in plasma. The difference between the rate of decay of the 14C-labeled fatty acid moiety, which represents all of the cholesteryl ester removed from plasma (0.48 pools/day) and the decay of the 3H-labeled cholesterol moiety, which represents the sum of cholesteryl ester removal and cholesterol reappearance (0.16 pools/day), is the fraction of the cholesteryl ester pool recycled per day (0.32 pools/day or 22.5 mg/kg per day). In other words, approximately 68% of the cholesterol moiety that was removed from plasma as cholesteryl oleate reappeared in the plasma cholesterol pool. These studies support the concept that an efficient reutilization cycle for plasma cholesterol occurs, i.e., the cholesteryl ester molecule can exit and the cholesterol moiety can re-enter plasma without effective equilibration of the cholesterol moiety with extravascular cholesterol pools.

Translational regulation of the L11 ribosomal protein operon of Escherichia coli: mutations that define the target site for repression by L1

The L11 ribosomal protein operon of Escherichia coli contains the genes for L11 and L1 and is feedback regulated by the translational repressor L1. The mRNA target site for this repression is located close to the Shine-Dalgarno sequence for the first cistron, rp1K (L11). By use of a random mutagenesis procedure we have isolated and characterized a series of point mutations in the L11 leader mRNA which eliminate or greatly diminish the regulation by L1. The mutations define a region essential for translational regulation upstream of the L11 Shine-Dalgarno sequence and identify a region of structural homology with the L1 binding site on 23S rRNA. These results are also consistent with the previously proposed model for the secondary structure of the L11 leader mRNA.

Secondary attachment site for bacteriophage lambda in the guaB gene of Escherichia coli

lambda gua transducing bacteriophages were used to identify and sequence the secondary attachment site for lambda in the guaB gene of Escherichia coli. The sequence matched the primary core sequence at nine positions, and a putative integrase binding-site overlapped the left core-arm junction. Recombinational crossover occurred between nucleotides -3 and +2 of the core region.

Comparison of beta-adrenoceptor selectivity of acebutolol and its metabolite diacetolol with metoprolol and propranolol in normal man

The beta-adrenergic selectivity of diacetolol, the major metabolite of acebutolol, has been compared with that of acebutolol, metoprolol and propranolol in 11 normal subjects. Bronchial and cardiac beta-adrenoceptor blockade were assessed on separate occasions after diacetolol 600 mg, acebutolol 400 mg, metoprolol 200 mg, propranolol 80 mg and placebo. Bronchial beta-adrenoceptor blockade was assessed as the displacement of the bronchodilator dose response curve to inhaled isoprenaline after each beta blocking drug compared to placebo and expressed as the dose ratio. Bronchodilatation was measured as change in specific airway conductance (sGaw) in the body plethysmograph. Cardiac beta-adrenoceptor blockade was assessed as the percentage reduction in exercise heart rate during the 5th minute of exercise at 70% of the subject's maximum work rate. There was a significant reduction in exercise heart rate with all 4 beta-blocking drugs when compared with placebo, 22% for diacetolol, 24% for acebutolol, 25% for propranolol and 28% for metoprolol. The reduction with metoprolol was significantly greater than the reduction with the other three beta-adrenoceptor antagonists. Mean dose ratios for the airway isoprenaline dose response curves after each of the 4 beta-blocking drugs were 2.4 for diacetolol, 2.7 for metoprolol, 8 for acebutolol and 72 for propranolol. The difference between diacetolol and metoprolol was not significant. Thus diacetolol appears to be more cardioselective than acebutolol and both are more cardioselective than propranolol in man. Metoprolol is probably more cardioselective than diacetolol though interpretation of the differences in exercise heart rate is complicated by the fact that diacetolol has some intrinsic sympathomimetic activity.

Nucleotide sequence and organisation of the gua promoter region of Escherichia coli

Overlapping restriction fragments of DNA carrying the gua promoter region of Escherichia coli have been cloned using promoter-probe plasmids. Antibiotic resistance conferred by the constructed plasmids is repressed by guanine and enhanced by adenine, two features characteristic of expression of the gua operon. The nucleotide sequence of these fragments reveals the gua promoter 43 bp upstream of the translational start codon for inosine 5'-monophosphate (IMP) dehydrogenase. The promoter is preceded by an A + T-rich region and several potential polymerase secondary binding sites, and is immediately followed by a G + C-rich discriminator, suggesting that the gua operon may be under stringent control. A sequence with twofold symmetry overlaps both promoter and discriminator and is therefore located where repressor binding could interfere with transcription initiation. A stem and loop can be formed from the leader mRNA, thus sequestering the ribosome-binding site.

Molecular cloning and characterisation of the gua regulatory region of Escherichia coli K12

The regulatory region of the gua operon of Escherichia coli is contained within a 2.1 kb EcoR1 restriction fragment isolated from a lambda pgua transducing phage. This DNA fragment was inserted into pPV33-II, a promoter-cloning vector, where it activated the gene(s) for tetracycline resistance. The level of tetracycline resistance conferred by the hybrid plasmid was reduced by the addition of guanine and increased by adenine, indicating the presence of the gua promoter. The cloned fragment codes for a polypeptide that complements in vivo the defective enzymes present in certain guaB mutants. This polypeptide was characterised using minicells and immunoprecipitation, and is presumed to correspond to the N-terminal region of IMP dehydrogenase.