PubMed Health⌕ Search

Biomedical subjects

J Brouwer

Publications and source records attributed to J Brouwer.

At least 55 records · Page 3Linked to original sources
PubMed1997

Transitions in the coupling of transcription and nucleotide excision repair within RNA polymerase II-transcribed genes of Saccharomyces cerevisiae.

The molecular mechanism of transcription-coupled nucleotide excision repair in eukaryotes is poorly understood. The identification of the dual role of basal transcription factor TFIIH in DNA repair and transcription provided a plausible link between both processes. However, TFIIH is not part of the elongating transcription complex, suggesting that additional components are required to recruit TFIIH when RNA polymerase II (RNAPII) stalls at the site of DNA damage. Previously, we have shown that the yeast Rad26 protein is involved in transcription-coupled DNA repair. This paper describes the differential contribution of the Rad26 protein to efficient removal of UV-induced cyclobutane pyrimidine dimers (CPDs) from transcribed DNA. Two distinct regions within the transcribed strand of RNAPII-transcribed genes are identified that differ in their requirement for the RAD26 gene product. Using high-resolution repair analysis, we determined the in vivo repair kinetics of cyclobutane pyrimidine dimers positioned around the transcription initiation site of RNAPII-transcribed genes RPB2 and URA3. Although transcription-coupled repair is severely reduced in rad26 mutants, lesions positioned in a small region immediately downstream of transcription initiation are efficiently removed in the absence of Rad26. The observed transition in repair characteristics is abrupt and in excellent agreement with the region where TFIIH dissociates from RNAPII in vitro, strongly suggesting an inverse correlation between TFIIH association and Rad26 requirement. These data suggest that a transcription repair coupling factor (Rad26/CSB) is required for efficient repair only during the elongating stages of RNAPII transcription.

Cell Cycle Proteins↗
PubMed1997

Transcription elongation factor S-II is not required for transcription-coupled repair in yeast.

Two different subpathways play a role in removal of UV-induced cyclobutane pyrimidine dimers (CPDs) by nucleotide excision repair (NER). The relatively slow global genome repair subpathway operates on all CPDs irrespective of their position in the DNA, whereas the transcription-coupled repair subpathway is responsible for the rapid removal of CPDs from transcribed strands. In Saccharomyces cerevisiae, the RAD26 gene is implicated in transcription-coupled repair. However, transcription-coupled repair is not completely absent in rad26 mutants, and therefore other gene products are possibly involved in this subpathway. Based on in vitro experiments with purified components, the transcription elongation factor S-II appeared to be a candidate for a function in transcription-coupled repair. To investigate a possible role of S-II in transcription-coupled repair in vivo in yeast, S-II null mutations were introduced into various genetic backgrounds differing in NER capacity. UV sensitivity was not altered by disruption of the S-II gene in a RAD+ (NER proficient) strain, or in rad26 (impaired in efficient transcription-coupled repair), rad7 (lacking global genome repair), or rad7 rad26 (lacking global genome repair, but having residual transcription-coupled repair capacity) mutants. Moreover, S-II did not influence the repair rate on the transcribed strand of the RPB2 gene, either in repair-proficient or in rad7 rad26 backgrounds. Hence, transcription-coupled repair is fully functional in yeast cells lacking the gene encoding S-II. Furthermore, S-II is not required for the Rad26-independent residual transcription-coupled repair in vivo.

DNA Repair↗
PubMed1997

Prognostic value of heart rate variability in chronic congestive heart failure secondary to idiopathic or ischemic dilated cardiomyopathy.

To study the prognostic value of heart rate (HR) variability in heart failure, risk assessment of clinical and HR variability parameters was performed in 159 patients with stable chronic heart failure. Besides low left ventricular ejection fraction, HR variability parameters reflecting impaired vagal tone (SDNN, pNN50) were found to predict an increased risk of cardiac death and death due to progressive pump failure.

Cardiomyopathy, Dilated↗
PubMed1997

Hemodynamic and autonomic effects of intravenous saterinone in patients with chronic heart failure.

In this study, the hemodynamic and neurohumoral/autonomic effects of intravenous saterinone (a selective phosphodiesterase type III inhibitor, with additional alpha 1-blocking properties) were evaluated. In a double-blind, placebo-controlled design, 36 patients with moderate to severe heart failure were studied (saterinone, n = 24; placebo, n = 12). Invasive hemodynamic measurements, by using right-heart catheterization, were performed, as well as measurement of plasma neurohormones and analysis of heart rate variability (HRV), to study drug influences on neurohumoral activation and autonomic tone. Systemic vascular resistance significantly decreased during saterinone infusion, accompanied by a decrease in systemic blood pressure (both p values < 0.05) and an increase in heart rate (p = 0.05). Filling pressures also decreased during saterinone, but this was statistically significant only for pulmonary capillary wedge pressure, whereas the cardiac index remained unaffected. Plasma neurohormones (norepinephrine, epinephrine, and renin activity) were not significantly influenced by saterinone. HRV analysis revealed no significant effect of saterinone on autonomic tone. These results suggest that intravenous saterinone has a significant vasodilating effect in patients with moderate to severe chronic heart failure (CHF), without exerting an adverse effect on the autonomic nervous system, as demonstrated by assessment of plasma neurohormones and HRV analysis.

Aged↗
PubMed1997

Analysis of atrial sensed far-field ventricular signals: a reassessment.

Accurate detection of the spontaneous far-field ventricular signal may be used to determine the ventricular activation, and hence, the interval from atrial stimulus to the ventricular R wave (AR interval) using a standard atrial pacing lead. This can be useful in developing a physiological atrial rate responsive (AAIR) pacemaker and in further improving DDD(R) pacing algorithms. In order to better characterize the atrial sensed far-field ventricular signal, 200 consecutive patients undergoing pacemaker implantation were studied. The amplitude of the far-field ventricular signal was significantly smaller than that of the atrial deflection. In all recordings, the slew rate of the atrial deflection was larger than that of the far-field ventricular signal. Subdivision of the recordings by electrode position, pocket location, or QRS duration on the surface ECG resulted in significantly different signal characteristics. The amplitude and slew rate of the far-field ventricular signal were significantly smaller in bipolar versus unipolar sensing. Atrial sensed far-field ventricular recordings could also be obtained in the case of ventricular pacing. Our results indicate that accurate sensing of the far-field ventricular signal from an atrial pacing lead is conceivable in most patients. The different signal characteristics in relation to parameters, such as electrode position, sensing mode, and pocket location, may be useful in determining the optimal conditions for signal sensing.

Cardiac Pacing, Artificial↗
PubMed1996

Prognostic value of heart rate variability during long-term follow-up in patients with mild to moderate heart failure. The Dutch Ibopamine Multicenter Trial Study Group.

OBJECTIVES: We sought to assess the prognostic value of heart rate variability measures, including Poincaré plots, in patients with mild to moderate chronic heart failure. BACKGROUND: Mortality is high in patients with heart failure, and many of them die suddenly. However, identification of high risk patients, particularly those with an increased risk for sudden death, has remained difficult. METHODS: We studied 95 patients with heart failure (mean [+/- SD] age 60 +/- 8 years, left ventricular ejection fraction 0.29 +/- 0.09, New York Heart Association functional class II [81%] and III [19%]) during up to 4 years of follow-up. Heart rate variability measures and Poincaré plots were obtained from 24-h Holter recordings. RESULTS: During follow-up, 17 (18%) of the 95 patients died. In 15 patients, death was cardiac related (11 patients experienced sudden death). None of the conventional time and frequency domain measures of heart rate variability were related to survival. In contrast, abnormal Poincaré plots identified a significantly higher risk for all-cause cardiac death (Cox proportional hazards ratio 5.7, 95% confidence interval [CI] 1.6 to 20.6, univariate analysis) and for sudden cardiac death (hazards ratio 6.8, 95% CI 1.5 to 31.4) compared with those with normal Poincaré plots. Patients with abnormal Poincaré plots were shown to have a lower left ventricular ejection fraction (0.26 +/- 0.10 vs. 0.31 +/- 0.08, p < 0.05) and higher plasma norepinephrine concentrations (506 +/- 207 pg/ml vs. 411 +/- 175 pg/ml, p < 0.05). In multivariate analysis, abnormal Poincaré plots still had independent prognostic value, both for all-cause cardiac mortality and for sudden cardiac death (hazards ratio 5.3, 95% CI 1.2 to 17.1, hazards ratio 4.5, 95% CI 1.0 to 27.5, respectively. CONCLUSIONS: Heart rate variability analysis, as assessed by Poincaré plots, has independent prognostic value in patients with mild to moderate chronic heart failure and identifies an increased risk for all-cause and sudden cardiac death in these patients.

Adolescent↗
PubMed1996

Cloning of Schizosaccharomyces pombe rph16+, a gene homologous to the Saccharomyces cerevisiae RAD16 gene.

The RAD16 gene is involved in the nucleotide excision repair of UV damage in the transcriptional silenced mating type loci (Terleth et al., 1990 and Bang et al., 1992) and in non-transcribed stands of active genes in Saccharomyces cerevisiae (Verhage et al., 1994). Using touchdown-PCR with primers derived from various domains of the S. cerevisiae Rad 16 protein, a specific Schizosaccharomyces pombe probe was isolated. This probe was used to obtain the complete RAD16 homologous gene from a S. pombe chromosomal bank. DNA sequence analysis of the rph16+ gene revealed an open reading frame of 854 amino acids. Comparison of the amino acid sequences of the Rhp16 and Rad16 proteins showed a high level of conservation: 68% similarity. The Rhp16 protein sequence contains the two Zn-finger motifs and the putative helicase domains as found in the Rad16 protein. Like the RAD16, the rph16+ gene is UV-inducible (Bang et al., 1995). In analogy with the rad16 mutant, the rhp16 disruption mutant is viable and grows normally, indicating that the gene does not have an essential function. The rhp16 disruption mutant is not sensitive for UV but is sensitive for cisplatin. The rhp16+ gene cloned behind the GAI 1 promoter partially complements the UV sensitivity and the defect in the non-transcribed strand DNA repair of a S. cerevisiae rad16 mutant, indicating functional homology between the rhp16+ and RAD16 genes. The structural and functional homology between the two genes suggests that the RAD16 dependent subpathway of NER for the repair of non-transcribed DNA is evolutionary conserved.

Adenosine Triphosphatases↗
PubMed1996

Transcription-coupled and global genome repair in the Saccharomyces cerevisiae RPB2 gene at nucleotide resolution.

Repair of UV-induced cyclobutane pyrimidine dimers (CPDs) was examined at single nucleotide resolution in the yeast Saccharomyces cerevisiae, using an improved protocol for genomic end-labelling. To obtain the sensitivity required for adduct detection in yeast, an oligonucleotide-directed enrichment step was introduced into the current methodology developed for adduct detection in Escherichia coli. With this method, heterogeneous repair of CPDs within the RPB2 locus is observed. Individual CPDs positioned in the transcribed strand are removed very efficiently with identical kinetics. This fast repair starts within 23 bases downstream of the transcription initiation site. The non-transcribed strand of the active gene exhibits slow repair without detectable repair variations between individual lesions. In contrast, CPDs positioned in the promoter region show profound repair heterogeneity. Here, CPDs at specific sites are removed very quickly, with comparable rates to CPDs positioned in the transcribed strand, while at other positions lesions are not repaired at all during the period studied. Interestingly, the fast repair in the promoter region is dependent on the RAD7 and RAD16 genes, as are the slowly repaired CPDs in this region and in the non-transcribed strand. This indicates that the global genome repair pathway is not intrinsically slow and at specific positions can be as efficient as the transcription-coupled repair pathway.

Adenosine Triphosphatases↗
PubMed1996

Repair of rDNA in Saccharomyces cerevisiae: RAD4-independent strand-specific nucleotide excision repair of RNA polymerase I transcribed genes.

Removal of UV-induced pyrimidine dimers from the individual strands of the rDNA locus in Saccharomyces cerevisiae was studied. Yeast rDNA, that is transcribed by RNA polymerase I(RNA pol I), is repaired efficiently, slightly strand-specific and independently of RAD26, which has been implicated in transcription-coupled repair of the RNA pol II transcribed RPB2 gene. No repair of rDNA is observed in rad1,2,3 and 14 mutants, demonstrating that dimer removal from this highly repetitive DNA is accomplished by nucleotide excision repair (NER). In rad7 and rad16 mutants, which are specifically deficient in repair of non-transcribed DNA, there is a clear preferential repair of the transcribed strand of rDNA, indicating that strand-specific and therefore probably transcription-coupled repair of RNA pol I transcribed genes does exist in yeast. Unexpectedly, the transcribed but not the non-transcribed strand of rDNA can be repaired in rad4 mutants, which seem otherwise completely NER-deficient.

DNA Repair↗
PubMed1996

Analysis of gene- and strand-specific repair in the moderately UV-sensitive Saccharomyces cerevisiae rad23 mutant.

The RAD23 gene of Saccharomyces cerevisiae is involved in nucleotide excision repair (NER) and mutations in this gene confer a moderate sensitivity to UV irradiation. However, no repair of either cyclobutane pyrimidine dimers (CPDs) and 6-4 photoproducts, the major types of lesions formed upon UV irradiation, was detectable during the first 4 h post UV irradiation in a rad23 mutant. rad23, like the rad7 and rad16 mutants, is not as UV sensitive as completely NER-deficient mutants. The rad7 and rad16 mutants are only partly defective in NER: non-transcribed strands are completely refractory to repair while transcription-coupled repair is not affected. To investigate whether the rad23 mutant has similar strand-specific repair characteristics we analyzed gene-specific CPD removal from several loci using strand-specific probes but did not detect any repair. The moderate UV sensitivity of rad23 mutants as compared to completely NER-deficient mutants is therefore not due to gene- or strand-specific removal of lesions, indicating that rad23 mutants do not have a similar repair defect as rad7 or rad16 mutants, but are presumably defective in general NER. The rad23 mutation does not suppress the high UV sensitivity of completely NER-deficient rad1 or rad14 strains. This demonstrates that the relatively high survival of rad23 mutants in not due to an increased tolerance for the lesions that seem to persist in the genome but rather requires some NER function.

Base Sequence↗
PubMed1996

Mismatch repair mutants in yeast are not defective in transcription-coupled DNA repair of UV-induced DNA damage.

Transcription-coupled repair, the targeted repair of the transcribed strands of active genes, is defective in bacteria, yeast, and human cells carrying mutations in mfd, RAD26 and ERCC6, respectively. Other factors probably are also uniquely involved in transcription-repair coupling. Recently, a defect was described in transcription-coupled repair for Escherichia coli mismatch repair mutants and human tumor cell lines with mutations in mismatch repair genes. We examined removal of UV-induced DNA damage in yeast strains mutated in mismatch repair genes in an effort to confirm a defect in transcription-coupled repair in this system. In addition, we determined the contribution of the mismatch repair gene MSH2 to transcription-coupled repair in the absence of global genomic repair using rad7 delta mutants. We also determined whether the Rad26-independent transcription-coupled repair observed in rad26 delta and rad7 delta rad26 delta mutants depends on MSH2 by examining repair deficiencies of rad26 delta msh2 delta and rad7 delta rad26 delta msh2 delta mutants. We found no defects in transcription-coupled repair caused by mutations in the mismatch repair genes MSH2, MLH1, PMS1, and MSH3. Yeast appears to differ from bacteria and human cells in the capacity for transcription-coupled repair in a mismatch repair mutant background.

Cell Cycle Proteins↗
PubMed1996

Molecular cloning and characterization of Saccharomyces cerevisiae RAD28, the yeast homolog of the human Cockayne syndrome A (CSA) gene.

Cockayne syndrome patients exhibit severe developmental and neurological abnormalities. Cells derived from these patients are sensitive to killing by UV radiation and do not support the rapid repair of the transcribed strand of transcriptionally active genes observed in cells from normal individuals. We report the cloning of the Saccharomyces cerevisiae homolog of the Cockayne syndrome A (CSA) gene, which we designate as RAD28. A rad28 null mutant does not manifest increased sensitivity to killing by UV or gamma radiation or to methyl methanesulfonate. Additionally, the rate of repair of the transcribed and nontranscribed strands of the yeast RPB2 gene in the rad28 mutant is identical to that observed in wild-type cells following exposure to UV light. As previously shown for rad7 rad26 and rad16 rad26 double mutants, the rad28 null mutant shows slightly enhanced sensitivity to UV light in the presence of mutations in the RAD7 or RAD16 gene. Both rad28 and rad26 null mutants are hypermutable following exposure to UV light.

Adenosine Triphosphatases↗
PubMed1996

Double mutants of Saccharomyces cerevisiae with alterations in global genome and transcription-coupled repair.

The nucleotide excision repair (NER) pathway is thought to consist of two subpathways: transcription-coupled repair, limited to the transcribed strand of active genes, and global genome repair for nontranscribed DNA strands. Recently we cloned the RAD26 gene, the Saccharomyces cerevisiae homolog of human CSB/ERCC6, a gene involved in transcription-coupled repair and the disorder Cockayne syndrome. This paper describes the analysis of yeast double mutants selectively affected in each NER subpathway. Although rad26 disruption mutants are defective in transcription-coupled repair, they are not UV sensitive. However, double mutants of RAD26 with the global genome repair determinants RAD7 and RAD16 appeared more UV sensitive than the single rad7 or rad16 mutants but not as sensitive as completely NER-deficient mutants. These findings unmask a role of RAD26 and transcription-coupled repair in UV survival, indicate that transcription-coupled repair and global genome repair are partially overlapping, and provide evidence for a residual NER modality in the double mutants. Analysis of dimer removal from the active RPB2 gene in the rad7/16 rad26 double mutants revealed (i) a contribution of the global genome repair factors Rad7p and Rad16p to repair of the transcribed strand, confirming the partial overlap between both NER subpathways, and (ii) residual repair specifically of the transcribed strand. To investigate the transcription dependence of this repair activity, strand-specific repair of the inducible GAL7 gene was investigated. The template strand of this gene was repaired only under induced conditions, pointing to a role for transcription in the residual repair in the double mutants and suggesting that transcription-coupled repair can to some extent operate independently from Rad26p. Our findings also indicate locus heterogeneity for the dependence of transcription-coupled repair on RAD26.

Adenosine Triphosphatases↗
PubMed1996

Cross-reactivity between Aspergillus fumigatus and Penicillium.

Rabbit anti-Aspergillus fumigatus, rabbit anti-Penicillium and sera from patients with precipitating antibodies against A. fumigatus or Penicillium were analyzed by means of inhibition experiments in ELISA (IgG) and (or) immunoblot analysis (IgG). Sera from healthy donors were also analyzed in ELISA inhibition and sera from patients with allergic bronchopulmonary aspergillosis (ABPA) in RAST (IgE) inhibition. Most sera from patients with precipitins against Penicillium gave anti-A. fumigatus ELISA titers in the same range as sera from patients with aspergillosis. Anti-Penicillium IgG reacted with several A. fumigatus antigens with molecular weights between 28 and 130 kD. This reaction could be inhibited by the carbohydrate fraction of A. fumigatus and by extracts of related fungi. The binding to Penicillium of IgE antibodies in sera from patients with ABPA could be inhibited by A. fumigatus almost as effectively as by Penicillium. The binding of these antibodies to A. fumigatus was only slightly affected by Penicillium antigens. The presence of IgG antibodies that cross-react with A. fumigatus may strongly affect the immunoblot patterns and ELISA results obtained with sera from patients with aspergillosis. Penicillium spp. probably belong to the major stimuli which induce the synthesis of so-called naturally occurring antibodies to A. fumigatus.

Animals↗
PubMed1995

Evaluation of importance of central effects of atenolol and metoprolol measured by heart rate variability during mental performance tasks, physical exercise, and daily life in stable postinfarct patients.

BACKGROUND: Physical exercise and mental work cause alterations in cardiac autonomic control. beta-Blockers protect the heart against stress, and this effect may be in part centrally mediated. In this context, the lipophilicity of the drug would be clinically relevant. METHODS AND RESULTS: Thirty postinfarct patients were randomized to receive 100 mg atenolol or 200 mg metoprolol CR in a double-blind, crossover manner, each for a 6-week period. Heart rate (HR) variability was used to study autonomic effects during mental and physical stress and to study circadian variations. Mean 24-hour HR decreased from 77 +/- 7 to 60 +/- 6 beats per minute after atenolol and to 62 +/- 6 beats per minute after metoprolol (P = .046). At baseline, mental performance tasks did not affect HR, but decreased HR variability (SDNN index from 51 +/- 26 to 30 +/- 13 milliseconds [ms], P < .001; high-frequency power from 130 +/- 143 to 110 +/- 125 ms2, P = .046; and low-frequency power from 538 +/- 447 to 290 +/- 275 ms2, P < .001). Both beta-blockers decreased HR during mental performance tasks (P < .001) and increased SDNN index and high-frequency power. Before treatment, bicycle exercise decreased HR variability; root-mean-square of successive difference decreased from 21 +/- 8 to 15 +/- 10 ms (P = .004). beta-Blockade could not prevent this decrease. No differences between atenolol and metoprolol were observed for absolute high- and low-frequency power or after adjustment for HR. Vagal blockade with methylatropine during chronic beta-blocker treatment nearly abolished all components of spectral power. HR was found to be the parameter most strongly affected by beta-blockade but not by an influence on vagal tone. No differences were found between atenolol and metoprolol. CONCLUSIONS: In stable postinfarct patients, chronic treatment with metoprolol and atenolol attenuates the reduction in HR variability induced by mental performance tasks, but the effects during exercise are limited. beta-Blockers do not appear to increase vagal tone in this stable patient group. The point of action in these patients is mainly a reduction in HR, probably due to a reduction in stress-induced sympathetic activation. Clinically significant differences between atenolol and metoprolol were absent, indicating that the degree of lipophilicity does not distinguish among the beta-blockers what their salutary effects are on HR variability during the specific challenges used.

Activities of Daily Living↗
PubMed1995

Usefulness of heart rate variability in predicting drug efficacy (metoprolol vs diltiazem) in patients with stable angina pectoris.

We investigated whether analysis of heart rate (HR) variability may be used to predict the efficacy of drug treatment of myocardial ischemia. In a double-blind, crossover study, 28 patients with stable angina pectoris, proven coronary artery disease, and myocardial ischemia during Holter monitoring received metoprolol controlled-release 200 mg once daily and diltiazem 60 mg 4 times daily. After a placebo run-in phase and after each treatment period, 72-hour Holter recordings were obtained for HR variability and ST-segment analysis. At baseline, the total duration of myocardial ischemia was 11.4 +/- 13.9 minutes (mean +/- SD per 24 hours), and the total number of episodes was 2.2 +/- 2.3. Metoprolol significantly reduced the total duration of ischemia by -8.7 minutes (95% CI -14.5 to -2.8) and the total number of episodes by -1.9 (-2.9 to -0.8) in patients with a low SD of normal-to-normal intervals at baseline (SDNN), using the median value of 50 ms as a cut-off value. In contrast, significant treatment effects were not observed in patients with a high SDNN at baseline. Similar results were obtained using baseline total power or low-frequency power, but not when using baseline heart rate. Diltiazem reduced the total duration of ischemia by -4.9 minutes (-9.7 to -0.1), but not the number of episodes. Moreover, in contrast to metoprolol, efficacy of diltiazem was not related to baseline HR variability. In conclusion, patients with reduced HR variability at baseline responded to treatment with metoprolol.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic beta-Antagonists↗