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Biomedical subjects

D L Bentley

Publications and source records attributed to D L Bentley.

At least 19 recordsLinked to original sources
PubMed1995

The transcriptional elongation inhibitor 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole inhibits transcription factor IIH-associated protein kinase.

Regulation of chain elongation by RNA polymerase II can have an important effect on gene expression (Bentley, D. (1995) Curr. Opin. Genet. Dev. 5, 210-216; Yankulov, K., Blau, J., Purton, T., Roberts, S., and Bentley, D. (1994) Cell 77, 749-759); however the mechanisms that control this step in transcription are not well understood. The adenosine analogue 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) has long been used as an inhibitor of RNA polymerase II elongation, but its target is not known. We show that DRB is a potent inhibitor of Cdk-activating kinase, associated with the general transcription factor TFIIH. Two other inhibitors of this kinase, H-7 and H-8, also inhibited transcriptional elongation. Furthermore, TFIIH kinase bound specifically to the herpes simplex virus VP16 activation domain which stimulates polymerase II elongation in addition to initiation (Yankulov, K., Blau, J., Purton, T., Roberts, S., and Bentley, D. (1994) Cell 77, 749-759). Our results suggest that DRB affects transcription by inhibiting the TFIIH-associated kinase and that this kinase functions in the control of elongation by RNA polymerase II.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1995

Regulation of transcriptional elongation by RNA polymerase II.

The process of transcription is a cycle of initiation, elongation and termination steps. Initiation and elongation can be rate-limiting for RNA synthesis, and recent evidence shows that transactivators can stimulate both these steps. A stable modification of the RNA polymerase II complex is probably required to convert it from a non-processive to a processive from.

Chromatin↗
PubMed1992

Distinct modes of transcription read through or terminate at the c-myc attenuator.

Premature termination of transcription by RNA polymerase II (pol II) occurs in the 5' region of many viral and cellular genes. Modulation of this process, or attenuation, is an important means of transcriptional control, but its mechanism is unknown. Using injected Xenopus oocytes, the efficiency of the mouse c-myc attenuator was tested when it was placed at various distances from the transcription initiation site. The attenuator functioned with each of six different pol II promoters tested; however, termination efficiency declined markedly when it was placed more than approximately 400 bases from the start site. This decline in attenuator function with distance from the start site coincided with increased sensitivity to the pol II inhibitor 5,6-dichloro-1-beta-D-ribofuranosyl benzimidazole (DRB). Thus transcription complexes situated further from the promoter appear to have a lower ability to recognize the attenuator and a greater sensitivity to DRB. Furthermore, polymerases which have read through one attenuation site have a reduced ability to terminate at a second site. The results imply that a discrete subset of elongation complexes is capable of premature termination, and that this subset exists only within the first few hundred bases of the transcription unit. Regulation of termination efficiency may be effected by changing the balance between the two modes of transcription committed either to read through or to terminate prematurely.

Animals↗
PubMed1992

A protein-binding site in the c-myc promoter functions as a terminator of RNA polymerase II transcription.

Termination of transcription not only allows polymerases that have completed RNA synthesis to recycle, but it also has important functions in transcriptional regulation and in preventing promoter interference. The molecular basis for termination by RNA polymerase II (pol II) is unclear, however. We have identified a termination site in the promoter region of the c-myc gene, whose function correlates with DNA binding by a nuclear factor. When the c-myc gene was transcribed in injected Xenopus oocytes or a HeLa nuclear extract, a fraction of RNA initiated at the first promoter, P1, terminated at two positions, T1A and T1B, which flank the TATA box of the second promoter, P2. T1B is a T-rich sequence that resembles previously identified attenuation sites, but T1A appears to represent a different class of termination site. T1A is situated approximately 10 bases upstream of an element that overlaps the P2 TATA box. Mutagenesis of this element affected both the efficiency and the position at which termination occurred. A 28-base sequence including this element caused a low level of termination when inserted into the alpha-globin gene in either orientation. This sequence bound a factor called TBF I (terminator-binding factor), whose binding specificity correlated with T1A terminator function. We suggest that TBF I may function as a pol II termination factor.

Animals↗
PubMed1991

Autosomal recessive chronic granulomatous disease caused by deletion at a dinucleotide repeat.

Chronic granulomatous disease (CGD) is a rare inherited condition rendering neutrophils incapable of killing invading pathogens. This condition is due to the failure of a multicomponent microbicidal oxidase that normally yields a low-midpoint-potential b cytochrome (cytochrome b245). Although defects in the X chromosome-linked cytochrome account for the majority of CGD patients, as many as 30% of CGD cases are due to an autosomal recessive disease. Of these, greater than 90% have been shown to be defective in the synthesis of a 47-kDa cytosolic component of the oxidase. We demonstrate here in three unrelated cases of autosomal recessive CGD that the identical underlying molecular lesion is a dinucleotide deletion at a GTGT tandem repeat, corresponding to the acceptor site of the first intron-exon junction. Slippage of the DNA duplex at this site may contribute to the high frequency of defects in this gene.

Amino Acid Sequence↗
PubMed1990

Characterization of the 47-kilodalton autosomal chronic granulomatous disease protein: tissue-specific expression and transcriptional control by retinoic acid.

A full-length cDNA clone was isolated for the 47-kilodalton (kDa) subunit of the NADPH oxidase system, whose absence is responsible for the most common form of autosomally inherited chronic granulomatous disease (CGD). It encodes a 44.7-kDa polypeptide, which contains two src homology (SH3) domains and several possible sites for phosphorylation by protein kinase C. We speculate that the SH3 domains may interact with the Rap1 protein associated with cytochrome b-245 (M.T. Quinn, C.A. Parkes, L. Walker, S. Orkin, M. Dinauer, and A. Jesaitis, Nature [London] 342:198-200, 1989). An antiserum raised to the predicted C terminus of the protein detects a polypeptide with an apparent molecular mass of 47 kDa in normal neutrophil granulocytes but not in those from patients with autosomal CGD. The antibody has been used to show that the protein associates with the vacuolar membrane and is phosphorylated in response to phorbol ester treatment. Analysis of a number of tissue types and cell lines shows that expression of the gene is confined to phagocytic cells and B lymphocytes. This observation suggests that patients with CGD may also have a defect in lymphocyte function. p47 protein and mRNA levels increase during retinoic acid-induced neutrophil differentiation of HL60 cells. Nuclear run-on transcription assays show that the gene for p47 is induced at the transcriptional level in a cycloheximide-insensitive manner. These data indicate that this gene is a primary target for regulation by retinoic acid.

Amino Acid Sequence↗
PubMed1990

Uterine activity compared with symptomatology in the detection of preterm labor.

The relative contribution of uterine activity obtained by home monitoring with a guard ring tocodynamometer compared with seven specific signs and symptoms reported during patient/nurse contact as an aid in detecting preterm labor has not been studied. In this prospective, multicenter study, patients at risk for developing early labor who were randomized to receive home uterine activity monitoring and perinatal nursing support were assessed. The initiator of provider contact (uterine activity detected on routine transmission, patient-perceived signs and symptoms of preterm labor during perinatal nurse contact, or both) resulting in a diagnosis of preterm labor was recorded. Contraction data were then analyzed for an association with preterm labor. There was a strong association of increased uterine activity (four or more contractions per hour) on a repeat monitoring strip with preterm labor (P less than .001). Among patients diagnosed with preterm labor, 31% had increased uterine activity detected on a routine transmission without patient-reported signs and symptoms, compared with 24% who were diagnosed as the result of patient-reported symptoms without increased uterine activity. Daily objective uterine activity data alone have greater incremental value over and above other signs and symptoms as an aid to the physician in diagnosing preterm labor.

Female↗
PubMed1990

The contribution of symptomatology and/or uterine activity to the incidence of unscheduled visits.

Home uterine activity monitoring and perinatal nursing support have been shown to be associated with a decrease in preterm births with no increase in the number of unscheduled patient visits. This prospective, randomized multicenter study compared the frequency of unscheduled visits in patients receiving home uterine activity monitoring and perinatal nursing support with that of patients receiving education regarding the detection and reporting of preterm labor symptomatology. The contribution of patient-reported signs and symptoms versus objective uterine activity data to unscheduled visits is assessed. The overall frequency of unscheduled visits was similar in both groups. In the home uterine activity monitoring and perinatal nursing support group, the contributions of uterine activity versus signs and symptoms to the diagnosis of preterm labor were equal, with 36% of patients diagnosed with preterm labor sent to the physician for increased uterine activity and 36% for signs and symptoms. The sensitivity for the group receiving monitoring and nursing support in detecting preterm labor was 93%. The majority of false-positive visits were associated with patient symptoms. These data show that this combination service does not lead to a clinically significant increase in unscheduled visits. Further, the visits resulting from the combination service provide a sensitive predictive method to aid physicians in detecting early labor.

Clinical Trials as Topic↗
PubMed1990

Relationship of uterine contractility to preterm labor.

An increased uterine contraction rate is associated with preterm labor. The contraction rate in individual patients, however, has not been evaluated critically as to its predictive value in forecasting early labor. In this randomized multicenter study, 105 patients at high risk for preterm delivery monitored their contraction rate at home on a daily basis. An analysis was conducted to determine the association of at least four contractions per hour on a routine strip followed by at least four contractions per hour on a repeat tracing with subsequent preterm labor. Using this threshold, 70% of the patients were correctly classified. This contraction rate resulted in a sensitivity of 57%, a specificity of 80%, a positive predictive value of 72%, and a negative predictive value of 68%. A threshold rate of at least four contractions per hour on a remonitor strip identifies a patient at increased risk for preterm labor (P = .003).

Cardiotocography↗
PubMed1990

Home uterine activity monitoring is associated with a reduction in preterm birth.

The value of home uterine activity monitoring plus perinatal nursing support in the prevention of preterm birth among high-risk patients has been demonstrated by several studies. Other reports with less stringent guidelines and less intensive nursing contact have questioned the contribution of home uterine activity monitoring and perinatal nursing support to a preterm birth prevention program. In this large, prospective, randomized multicenter study, patients were assigned to receive either daily monitoring and nursing contact or a preterm birth prevention program including intensive education and more frequent prenatal visits. Among the monitored patients, there was a significant increase in early detection of preterm labor (2 cm or less), successful tocolysis, and prolongation of pregnancy to term. Thirty-one percent of these diagnoses of preterm labor resulted from evaluation of increased uterine activity without associated patient-perceived symptoms. We conclude that a program of daily uterine activity monitoring and perinatal nursing support results in earlier diagnosis of preterm labor and subsequently more effective tocolysis.

Cardiotocography↗
PubMed1990

Preventing preterm birth in twin gestation: home uterine activity monitoring and perinatal nursing support.

In this investigation, 45 women with twin gestations in four centers were randomly assigned to either daily home uterine activity monitoring and perinatal nursing support (19) or an education group (26). Patients in the home uterine activity monitoring and perinatal nursing support group monitored uterine activity twice daily, transmitted the data each day, and had 24 hour-a-day access to nursing support. Education patients were counseled regarding the common signs and symptoms of preterm labor. Both groups had scheduled prenatal visits at least every 2 weeks. Sixteen (62%) of the education group and 14 (74%) of the home uterine activity monitoring and perinatal nursing support group developed preterm labor, values that were not significantly different. Of the monitored group who experienced preterm labor, all 14 were dilated 3 cm or less at diagnosis of the first preterm labor, compared with ten of 16 in the education group (P = .01; one-tailed Fisher test). The mean cervical dilatation at the first preterm labor episode in the group receiving daily monitoring and contact (1.6 cm) was significantly less (P = .01) than that in the education group (2.9 cm). Thus, fewer preterm births were recorded in the home uterine activity monitoring and perinatal nursing support group and significantly fewer patients delivered because of failed tocolysis (P = .03).

Adult↗
PubMed1990

Management of preterm labor patients at home: does daily uterine activity monitoring and nursing support make a difference?

Daily home uterine activity monitoring and perinatal nursing support were compared with standard care in managing patients with recurrent preterm labor during the current pregnancy in an effort to reduce preterm birth. Sixty-seven successfully treated preterm labor patients were randomly assigned in this multicenter study to daily home uterine activity monitoring and perinatal nursing support or to a standard-care group. Recurrent preterm labor occurred in 15 (45%) of monitored patients and 19 (56%) of standard-care patients. The risk of preterm birth (before 37 weeks) for patients with recurrent preterm labor was significantly reduced (P = .025) in the monitored group (seven, or 47%) compared with the standard-care group (16, or 84%). The relative risk of delivering because of failed tocolysis was 2.8 for the standard-care group versus the monitored group. There were no patients in the monitored group who delivered at the first recurrence of preterm labor for failed tocolysis. The data suggest that home uterine activity monitoring and perinatal nursing support are helpful in achieving term birth through earlier detection and treatment of recurrent preterm labor.

Adult↗
PubMed1990

Uterine activity characteristics in multiple gestations.

The frequency of uterine contractions has been shown to be increased during the 24-48 hours before the diagnosis of preterm labor in singleton gestations. Experience has indicated that there is also an increase in baseline uterine activity in twin gestations beyond that seen in women with singleton pregnancies. In this study, patients with twin gestations (39), triplet pregnancies (20), and quadruplets (ten) were monitored in the home daily for uterine activity. The results indicate that uterine activity was increased slightly within 48 hours of the onset of their initial preterm labor episode and significantly increased over baseline during the 24 hours preceding the diagnosis of preterm labor. This uterine activity led to evaluation for preterm labor before advanced dilatation occurred so that the majority of patients continued their pregnancy for more than 48 hours after diagnosis. Tocolytics did not have an effect on the crescendo of uterine activity preceding preterm labor. In this study, the crescendo of uterine activity occurred in multifetal gestations within 24 hours of preterm labor, as has been described for singleton pregnancies.

Female↗
PubMed1989

Accurate, TATA box-dependent polymerase III transcription from promoters of the c-myc gene in injected Xenopus oocytes.

We have investigated the factors that permit a gene normally transcribed by RNA polymerase II to be transcribed by RNA polymerase III. It was shown previously that the human c-myc gene could be transcribed in vitro and in Xenopus oocytes by both alpha-amanitin-sensitive and alpha-amanitin-resistant polymerases, probably corresponding to polymerase II and polymerase III. We confirmed this observation in microinjected oocytes and showed that the alpha-amanitin-resistant transcription of c-myc was competed by known polymerase III genes. Polymerase III transcription of c-myc was very inefficient compared to other polymerase III genes, however, and was observed only when large amounts of template DNA were injected. At lower DNA concentrations the gene was transcribed, exclusively by polymerase II. In contrast, the adenovirus major late promoter was not transcribed by polymerase III. The 5' ends of polymerase III RNAs were almost indistinguishable from those of polymerase II RNAs initiating at the P1 and P2 promoters of the human and mouse c-myc genes. Furthermore, point mutations in the TATA box of the human P2 promoter greatly reduced polymerase III activity. At this promoter, therefore, polymerase II and polymerase III recognize a common element, the TATA box, which probably plays an important role in specifying the start site of transcription for both polymerases. We suggest that the highly accurate though inefficient mimicry of polymerase II by polymerase III at the c-myc promoters reflects the common evolutionary origin of these two enzymes.

Animals↗
PubMed1988

Sequence requirements for premature termination of transcription in the human c-myc gene.

We have used the Xenopus oocyte injection system to investigate the sequence requirements of premature termination of transcription within the human c-myc gene. We show that in the oocyte, truncated RNAs are produced by RNA polymerase II with 5' ends at the P1 and P2 promoters and 3' ends at two T stretches (sites I and II) near the exon 1/intron 1 junction. The location of these 3' ends is consistent with the site of the block to c-myc transcription identified by nuclear runoff assays in human cells and confirmed in dissected nuclei of injected oocytes. Evidence is presented that transcriptional termination rather than RNA processing produces these short c-myc RNAs. Deletion analysis of site I reveals that sequences upstream of the T stretch determine the site of 3' end formation, and that the stretch of T's on the sense DNA strand is not required for termination. The sequences specifying termination reside within a 95 base region located -130 to -35 relative to the exon 1/intron 1 boundary. The termination activity of these sequences is orientation-dependent and functions downstream of the HSV-TK promoter.

Animals↗
PubMed1988

A non-AUG translational initiation in c-myc exon 1 generates an N-terminally distinct protein whose synthesis is disrupted in Burkitt's lymphomas.

The c-myc gene comprises three exons with a single large AUG-initiated open reading frame extending from exon 2 through exon 3. Exon 1 lacks any AUG codons. Cells from a wide range of species produce two c-myc proteins that, while highly related, do not appear to arise from posttranslational interconversion. To understand the origin of the two proteins, we mapped them and analyzed the in vitro protein-coding capacity of c-myc cDNAs. Our findings show that the two proteins are derived from alternative translational initiations at the exon 2 AUG and at a non-AUG codon near the 3' end of exon 1, resulting in the production of proteins with distinct N termini. In Burkitt's lymphomas, the removal or specific mutation of exon 1 in c-myc translocations correlates with suppression of synthesis of the larger protein, and thus may contribute to the oncogenic activation of c-myc.

Animals↗
PubMed1986

Novel promoter upstream of the human c-myc gene and regulation of c-myc expression in B-cell lymphomas.

A new promoter of the human c-myc gene called P0, with multiple RNA start sites, was mapped over 500 bases upstream of the two previously identified promoters, P1 and P2. Sequencing full-length cDNA clones of P0 RNAs revealed two open reading frames upstream of that for the P64c-myc protein. P0 RNA is located on polyribosomes and released by puromycin, indicating that it functions as an mRNA. In vitro translation of RNA synthesized from the cloned cDNAs predicts that P0 transcripts are translated into a novel 12.5-kilodalton protein corresponding to the first open reading frame. The regulation of P0 RNA was studied in the B-cell lymphoma cell line Manca, in which only the translocated c-myc allele lacking exon 1 was thought to be active. However, we found that P0 transcription and the DNase I-hypersensitive site associated with this promoter persist on the untranslocated allele, even though P1/P2 transcription as measured by a nuclear runoff assay was repressed. These results suggest that allelic exclusion of c-myc expression in this B-cell lymphoma is caused by a repression of transcription which is specific to the P1/P2 promoters. We previously reported a block to elongation of transcription near the 3' end of exon 1 in the wild-type c-myc gene, which results in an excess of exon 1 over exon 2 transcription (5a). In contrast, we found that in the Daudi B-cell lymphoma, which retains exon 1 in the active allele, equimolar transcription of exons 1 and 2 occurs. This result suggests a model for the activation of c-myc in B-cell lymphomas.

Amino Acid Sequence↗