The means to bind the ends.
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Binding Sites↗
Biomedical subjects
D Shore
Publications and source records attributed to D Shore.
Evidence that the transcriptional regulators SIN3 and RPD3, and a novel gene (SDS3) with similar functions, are involved in transcriptional silencing in S. cerevisiae.
In a screen for extragenic suppressors of a silencing defective rap 1s hmr delta A strain, recessive mutations in 21 different genes were found that restored repression to HMR. We describe the characterization of three of these SDS (suppressors of defective silencing) genes. SDS16 and SDS6 are known transcriptional modifiers, SIN3(RPD1/UME4/SDI1/GAM2) and RPD3(SDI2), respectively, while the third is a novel gene, SDS3. SDS3 shares the meiotic functions of SIN3 and RPD3 in that it represses IME2 in haploid cells and is necessary for sporulation in diploid cells. However, sds3 mutations differ from sin3 and rpd3 mutations in that they do not derepress TRK2. These sds mutations suppress a variety of cis- and trans-defects, which impair the establishment of silencing at HMR. Any one of the sds mutations slightly increases telomere position effect while a striking synergistic increase in repression is observed in a rap 1s background. Epistasis studies suggest that SDS3 works in a different pathway from RPD3 and SIN3 to affect silencing at HMR. Together these results show that defects in certain general transcriptional modifiers can have a pronounced influence on position-effect gene silencing in yeast. Mechanisms for this increase in position effect are discussed.
Fungal Proteins↗
SUM1-1, a dominant suppressor of SIR mutations in Saccharomyces cerevisiae, increases transcriptional silencing at telomeres and HM mating-type loci and decreases chromosome stability.
Transcriptional silencing in the yeast Saccharomyces cerevisiae occurs at HML and HMR mating-type loci and telomeres and requires the products of the silent information regulator (SIR) genes. Recent evidence suggests that the silencer- and telomere-binding protein Rap1p initiates silencing by recruiting a complex of Sir proteins to the chromosome, where they act in some way to modify chromatin structure or accessibility. A single allele of the SUM1gene (SUM1-1) which restores silencing at HM loci in strains mutant for any of the four SIR genes was identified a number of years ago. However, conflicting genetic results and the lack of other alleles of SUM1 made it difficult to surmise the wild-type function of SUM1 or the manner in which the SUM1-1 mutation restores silencing in sir mutant strains. Here we report the cloning and characterization of the SUM1 gene and the SUM1-1 mutant allele. Our results indicate that SUM1-1 is an unusual altered-function mutation that can bypass the need for SIR function in HM silencing and increase repression at telomeres. A sum1 deletion mutation has only minor effects on silencing in SIR strains and does not restore silencing in sir mutants. In addition to its effect on transcriptional silencing, the SUM1-1 mutation (but not a sum1 deletion) increases the rate of chromosome loss and cell death. We suggest several speculative models for the action of SUM1-1 in silencing based on these and other data.
Amino Acid Sequence↗
Ethical principles and informed consent: an NIMH perspective.
In conclusion, several points are worth emphasizing at this juncture: 1. Clinical researchers must attend to a set of ongoing concerns in new ways and reconsider how best to explain research protocols to potential subjects. Consent procedures and documents 5 or 10 years old may not be considered adequate by current standards. It is clearly important to ensure that consent documents, and the process by which informed consent is obtained and maintained, are state-of-the-art. 2. Many valuable sources of information are available to help researchers, family members, and potential participants learn about proper informed consent. NIMH is taking steps to improve this educational process. Members of IRBs are educated through conferences, newsletters, case books, etc. OPRR (May 1994) has also provided considerable information relevant to informed consent in clinical research. OPRR and NIMH staff may be useful sources of information concerning informed consent. 3. Research on competency and the consent process itself is needed so we can compare what was explained with what was understood and learn what research subjects want to know, what they believe has occurred, and why. 4. Progress in discovering the underlying causes of schizophrenia and other severe mental disorders, and improving their treatment, will require scientifically rigorous studies involving people affected by these disorders. Attempts to prohibit competent people with mental disorders from making decisions about participating in research protocols seem misguided, paternalistic, and stigmatizing. If we are to improve the treatment of severe mental disorders, clinical research is essential, including research that is not likely to directly benefit each individual participating. 5. This is a time of great opportunity for clinical research. New medications being tested have the potential to revolutionize the treatment of severe mental disorders. During recent years, a number of large scale projects have been focusing on underlying genetic vulnerability factors that may shed light on the etiology of these disorders, with profound implications for diagnosis, treatment, and eventually even prevention. Unfortunately, clinical research is also under attack on several fronts, including concerns about consent and the protection of human subjects with mental disorders. If we do not take steps now to ensure that the process by which we protect and inform research participants is state-of-the-art, the very progress we seek will be at risk.
Animals↗
Aging. Silence is golden.
A pioneering genetic analysis of aging in yeast has revealed that a protein complex known to play an essential role in transcriptional silencing at mating-type loci and telomeres also controls aging and stress resistance.
Cell Division↗
Characterization of right ventricular diastolic performance after complete repair of tetralogy of Fallot. Restrictive physiology predicts slow postoperative recovery.
BACKGROUND: Prolonged postoperative recovery caused by a low cardiac output state occurs in some patients after complete repair of tetralogy of Fallot. Biventricular systolic function is usually well preserved in these patients. The contribution of impaired diastolic function, particularly of the right ventricle, has not been studied in detail; therefore, we performed a prospective study of right ventricular diastolic function in this patient group. METHODS AND RESULTS: We studied biventricular systolic and diastolic function using Doppler echocardiographic examination. Tricuspid valve, superior vena caval, pulmonary arterial, and mitral valve Doppler spectrals were obtained during the first postoperative day in 35 patients aged 6 months to 45 years who underwent complete repair of tetralogy of Fallot. Biventricular systolic function was grossly normal in all patients. Isolated restrictive right ventricular physiology characterized by pulmonary arterial antegrade flow coincident with atrial systole and associated with prominent retrograde superior vena caval flow was seen in 17 of the 35 patients (group 1). This flow was augmented during the expiratory phase of positive pressure ventilation and abolished or greatly diminished during the inspiratory phase (P < .001). An increase in the duration of pulmonary regurgitation occurred during the inspiratory phase of positive pressure ventilation in these patients (P < .01). All patients with right ventricular restriction had a clinical picture compatible with a low cardiac output state, requiring prolonged stays in intensive care and the hospital. Clinical improvement was mirrored by resolution of the Doppler markers of right ventricular restriction in most of the patients. CONCLUSIONS: Isolated right ventricular restriction is characterized by antegrade diastolic pulmonary arterial flow on Doppler echocardiography and is responsible for the slower postoperative course and clinical evidence of low cardiac output state in some patients after complete repair of tetralogy of Fallot.
Adolescent↗
Action of a RAP1 carboxy-terminal silencing domain reveals an underlying competition between HMR and telomeres in yeast.
RAP1 is a sequence-specific DNA-binding protein in yeast that can either repress or activate transcription. Previous studies have demonstrated a direct role for RAP1 in silencing at HM mating-type loci and telomeres. Here, we show that a small carboxy-terminal domain of RAP1 is sufficient to establish repression when fused to the GAL4 DNA-binding domain (GBD) and targeted to mutated HMR silencers containing GAL4 DNA-binding sites. Silencing by GBD/RAP1 hybrids, like normal silencing at HMR, requires the trans-acting factors SIR2, SIR3, and SIR4. However, GBD/RAP1-mediated silencing is independent of SIR1, whose product is normally required for the establishment of repression at HMR. Targeted silencing also displays an unusual response to silencing-defective rap1s mutations. The incorporation of a rap1s missense mutation into GBD/RAP1 hybrids can improve targeted silencing, yet wild-type GBD/RAP1 hybrids fail to establish repression in strains in which the endogenous RAP1 locus carries a rap1s mutation. In addition, we find that telomeric silencing is increased in rap1s strains. We propose that the rap1s mutation creates an HMR-specific silencing defect by shifting a balance between silencing at HMR and telomeres in favor of telomeric silencing. This balance is regulated by telomere length and by interactions between the RAP1 carboxyl terminus and both RIF1 and SIR4 proteins. In support of this model, we show that abnormally long telomeres antagonize silencing at HMR and a rap1s hybrid protein displays a strengthened interaction with SIR4 in a two-hybrid assay.
Base Sequence↗
Suppressors of defective silencing in yeast: effects on transcriptional repression at the HMR locus, cell growth and telomere structure.
To identify factors that affect transcriptional silencing at the HMR mating-type locus in yeast, we characterized a set of extragenic suppressor mutations that restore metastable repression in cells containing both a mutant silencer-binding protein (rap1s) and a mutated silencer element (hmr delta A). A total of 57 suppressors comprising 21 different complementation groups was identified. This report describes a detailed genetic analysis of these suppressors of defective silencing (sds) mutants. The sds mutants fall into several distinct categories based on secondary phenotypes, such as their ability to suppress the rap1s telomere lengthening phenotype, general effects on telomere length, temperature-dependent growth defects, and the ability to bypass the requirement for cis regulatory elements at the HMR-E silencer. One particular mutant, sds4-1, strongly suppresses the rap1s silencing defect, restores telomeres to nearly wild-type length, and displays a severe growth defect at all temperatures. SDS4 mutations also suppress the silencing defect caused by mutations in the RAP1-interacting factor RIF1. We cloned the SDS4 gene and show that it is identical to GAL11(SPT13), which encodes a component of a protein complex that mediates transcriptional activation. Possible mechanism(s) of suppression by sds4 and the other sds mutations is discussed.
Chromosomes, Fungal↗
Molecular and genetic analysis of the toxic effect of RAP1 overexpression in yeast.
Rap1p is a context-dependent regulatory protein in yeast that functions as a transcriptional activator of many essential genes, including those encoding ribosomal proteins and glycolytic enzymes. Rap1p also participates in transcriptional silencing at HM mating-type loci and telomeres. Overexpression of RAP1 strongly inhibits cell growth, perhaps by interfering with essential transcriptional activation functions within the cell. Here we report a molecular and genetic analysis of the toxic effect of RAP1 overexpression. We show that toxicity does not require the previously defined Rap1p activation and silencing domains, but instead is dependent upon the DNA-binding domain and an adjacent region of unknown function. Point mutations were identified in the DNA-binding domain that relieve the toxic effect of overexpression. Two of these mutations can complement a RAP1 deletion yet cause growth defects and altered DNA-binding properties in vitro. However, a small deletion of the adjacent (downstream) region that abolishes overexpression toxicity has, by itself, no apparent effect on growth or DNA binding. SKO1/ACR1, which encodes a CREB-like repressor protein in yeast, was isolated as a high copy suppressor of the toxicity caused by RAP1 overexpression. Models related to the regulation of Rap1p activity are discussed.
Alleles↗
Clinical implications of clozapine discontinuation: report of an NIMH workshop.
In September 1994, the National Institute of Mental Health convened a group of scientists to discuss the clinical effects of rapid clozapine discontinuation, especially in light of the introduction of risperidone for the treatment of schizophrenia. Despite concern over recent reports of clinical deterioration (psychotic exacerbations, somatic withdrawal symptoms, and extrapyramidal side effects) in a few patients abruptly discontinued from clozapine, there is currently insufficient information to determine the magnitude of the problems associated with clozapine withdrawal. However, clinicians are reminded that the withdrawal schedule for clozapine indicates a gradual tapering schedule (unless the patient is experiencing severe side effects); that switching patients from clozapine to risperidone does not mean that such tapering is unnecessary; and that the use of risperidone may not produce all of the same effects as clozapine in some treatment-refractory patients.
Antipsychotic Agents↗
Disturbance of normal cell cycle progression enhances the establishment of transcriptional silencing in Saccharomyces cerevisiae.
Previous studies have indicated that mutation of RAP1 (rap1s) or of the HMR-E silencer ARS consensus element leads to metastable repression of HMR. A number of extragenic suppressor mutations (sds, suppressors of defective silencing) that increase the fraction of repressed cells in rap1s hmr delta A strains have been identified. Here we report the cloning of three SDS genes. SDS11 is identical to SWI6, a transcriptional regulator of genes required for DNA replication and of cyclin genes. SDS12 is identical to RNR1, which encodes a subunit of ribonucleotide reductase. SDS15 is identical to CIN8, whose product is required for spindle formation. We propose that mutations in these genes improve the establishment of silencing by interfering with normal cell cycle progression. In support of this idea, we show that exposure to hydroxyurea, which increases the length of S phase, also restores silencing in rap1s hmr delta A strains. Mutations in different cyclin genes (CLN3, CLB5, and CLB2) and two cell cycle transcriptional regulators (SWI4 and MBP1) also suppress the silencing defect at HMR. The effect of these cell cycle regulators is not specific to the rap1s or hmr delta A mutation, since swi6, swi4, and clb5 mutations also suppress mutations in SIR1, another gene implicated in the establishment of silencing. Several mutations also improve the efficiency of telomeric silencing in wild-type strains, further demonstrating that disturbance of the cell cycle has a general effect on position effect repression in Saccharomyces cerevisiae. We suggest several possible models to explain this phenomenon.
Cell Cycle↗
Shared care between general practitioners and urologists in the management of benign prostatic hyperplasia: a survey of attitudes among clinicians.
Recent community-based population surveys have revealed a much greater prevalence of benign prostatic hyperplasia than previously suspected. From these data it has been projected that there may be more than 2 million men in the UK whose quality of life is to some extent impaired by this disorder. Since there are only 330 fully trained urologists in this country it will not be feasible for every individual presenting with prostatism to be assessed by a specialist. In an attempt to provide a more rational basis from which family practitioners can decide whether or not to refer a patient for a specialist opinion a 'shared care' flow diagram was developed and assumptions contained within field tested by means of a postal questionnaire which was sent to 2020 urologists, family practitioners and other interested clinicians. There was general agreement with most of the precepts set out in the flow diagram, the main exception was a rejection of the suggestion that every patient with prostatism should have a prostate-specific antigen level determined before referral. We conclude that there seems a consensus among respondents that a shared care approach to the management of BPH may both improve the standard of care provided in this area by family practitioners and allow hard pressed urologists to focus greater attention on those patients whose conditions require surgical expertise to resolve.
Attitude of Health Personnel↗
Psychiatric genetic research at the National Institute of Mental Health.
For some time it has been known through the results of family, twin, and adoption studies that heredity appears to play a significant causal role in many mental disorders, including schizophrenia, bipolar disorder, and other mood disorders, Alzheimer's Disease, panic disorder, obsessive compulsive disorder, autism, dyslexia, and Tourette's Syndrome. The precise patterns of inheritance of these complex disorders have not been determined, nor have the relevant genes been localized or cloned. Because the genetics are complex and because there is also clearly an environmental contribution to behavior, we expect the analysis of the genetics of mental illness to be arduous, and not quickly resolved. There are several compelling reasons to continue to focus our attention on uncovering the genetic factors for severe mental illness. Prominent among these are the implications for better treatment of mental disorders. The National Institute of Mental Health supports a wide range of studies on psychiatric genetic research.
Brain Diseases↗
Evidence that a complex of SIR proteins interacts with the silencer and telomere-binding protein RAP1.
The maintenance of transcriptional silencing at HM mating-type loci and telomeres in yeast requires the SIR2, SIR3, and SIR4 proteins, none of which appear to be DNA-binding proteins. Here we show that SIR3 and SIR4 interact with a carboxy-terminal domain of the silencer, telomere, and UAS-binding protein RAP1. We identified SIR3 and SIR4 in a two-hybrid screen for RAP1-interacting factors and showed that SIR3 interacts both with itself and with SIR4. The interaction between RAP1 and SIR3 can be observed in vitro in the absence of other yeast proteins. Consistent with the notion that native SIR proteins interact with the RAP1 carboxyl terminus, we show that mutation of the endogenous SIR3 and SIR4 genes increases transcriptional activation by LexA/RAP1 hybrids. To test the importance of the RAP1-SIR3 interaction for silencing, we identified mutations in the RAP1 carboxyl terminus that either diminish or abolish this interaction. When introduced into the native RAP1 protein, these mutations cause corresponding defects in silencing at both HMR and telomeres. We propose that RAP1 acts in the initiation of transcriptional silencing by recruiting a complex of SIR proteins to the chromosome via protein-protein interactions. These data are consistent with a model in which SIR3 and SIR4 play a structural role in the maintenance of silent chromatin and indicate that their action is initiated at the silencer itself.
Bacterial Proteins↗
RAP1: a protean regulator in yeast.
The yeast protein RAP1 is a sequence-specific DNA-binding protein that binds to many promoters, to two elements that silence mating-type genes, and to [(C)1-3A]n tracts at telomeres. RAP1 is essential for cell viability and can function as either an activator or a repressor of transcription, depending upon the context of its binding site. Recent experiments suggest that its function may be determined by different sets of protein-protein interactions at promoters and silencers. At the ends of chromosomes, RAP1 plays an important role in both silencing (telomere position effect) and telomere structure.
DNA↗
Complete atrioventricular septal defect with tetralogy of Fallot: diagnosis and management.
OBJECTIVE: To report recent experience of patients with complete atrioventricular septal defect and tetralogy of Fallot, with emphasis on anatomical features, diagnosis, and management. DESIGN: Case notes were reviewed and patients were assessed at follow up by clinical examination and cross sectional and Doppler echocardiography. SETTING: Tertiary cardiothoracic referral centre. PATIENTS: Between 1987 and 1992 13 patients with atrioventricular septal defect and tetralogy of Fallot (12 with concordant and one with double outlet ventriculoarterial connections) underwent surgery; 10 underwent complete intracardiac repair. 11 patients had Down's syndrome. The complete diagnosis was established preoperatively by cross sectional echocardiography in all but one patient. A tri-leaflet left atrioventricular valve as seen in parasternal short axis views was the diagnostic feature of atrioventricular septal defect, with tetralogy of Fallot diagnosed from the presence of anterocephalad deviation of the outlet septum producing subvalvar pulmonary stenosis as seen in subcostal right anterior oblique views. INTERVENTIONS: Total correction consisted of closure of the atrioventricular septal defect by a combined right atrial and ventricular approach, reconstruction of the atrioventricular valves, and relief of the obstruction within the right ventricular outflow tract. Separate patches were used to close the atrial and ventricular septal defects. Modified Blalock-Taussig shunts were performed in three patients, who await intracardiac repair. Surgical correction was carried out at mean (range) age of 5 (2 to 15) years. MAIN OUTCOME MEASURES: Diagnostic methods, surgical results, and functional state after complete correction. RESULTS: The presence of an atrioventricular septal defect was missed preoperatively in one patient with tetralogy of Fallot. The characteristic goose neck deformity on the left ventriculogram was not present and the tri-leaflet nature of the left atrioventricular valve was not sought on echocardiography. Of the 10 patients who underwent complete repair, nine are alive and one died 34 days after operation with adult respiratory distress syndrome. Examination at necropsy showed an excellent surgical correction. Mean (range) follow up was 23 (8 to 48) months. All nine patients are alive and well (New York Heart Association Class 1). CONCLUSION: Accurate diagnosis and staged management with improved surgical techniques have lowered mortality of this complex combination of cardiac defects. The current policy of this group is to recommend a systemic to pulmonary arterial shunt procedure for symptomatic children younger than 2 years and total correction in older children.
Adolescent↗
Targeting of SIR1 protein establishes transcriptional silencing at HM loci and telomeres in yeast.
Previous studies suggest that the yeast SIR1 protein is involved in the establishment of transcriptional silencing at the HM mating-type loci. Here we show that a GAL4 DNA-binding domain-SIR1 hybrid protein (GBD-SIR1), when targeted to an HMR locus containing GAL4-binding sites (UASG), can establish silencing and bypass the requirement for the silencer element HMR-E. Silencing mediated by GBD-SIR1 requires the trans-acting factors that normally participate in repression, namely, SIR2, SIR3, SIR4, and histone H4. However, GBD hybrids with SIR2, SIR3, or SIR4 cannot establish silencing. Telomeric silencing, which does not require SIR1 and is normally unstable, is greatly improved by tethering GBD-SIR1 to the telomere. These experiments support a model in which native SIR1 protein is brought to the HM loci by proteins bound to the silencers. Telomeres appear to lack the ability to recruit SIR1, and that is why telomeric silencing is unstable.
Crosses, Genetic↗
Legal and ethical issues in psychiatric genetic research.
Genetic research may uncover the causes of severe mental disorders, and many projects have been undertaken to locate the genes responsible for schizophrenia, bipolar disorder, and Alzheimer disease. A number of sensitive legal and ethical issues have been raised, including 1) protection of confidential data concerning research subjects; 2) the assessment of types and degree of risk to subjects who participate in such studies; 3) the legal and ethical acceptability of substituted judgement on behalf of patients who may not be competent to provide informed consent; and 4) the separation of research and clinical roles in areas such as genetic counseling. Federal regulations and other guidelines are of limited value in dealing with such concerns, and many important human subjects issues will need to be dealt with by the investigator, subject to approval by a local Institutional Review Board. There does seem to be general agreement that informed consent must be obtained, potential risks of research need to be minimized, and confidentiality of sensitive data must be protected.
Advance Directives↗