Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.6 (RNA polymerase)
 34,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

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.
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PMID:Distinct modes of transcription read through or terminate at the c-myc attenuator. 137 47

A conditional block to transcriptional elongation is an important mechanism for regulating c-myc gene expression. This elongation block within the first c-myc exon was defined originally in mammalian cells by nuclear run-on transcription analyses. Subsequent oocyte injection and in vitro transcription analyses suggested that sequences near the end of the first c-myc exon are sites of attenuation and/or premature termination. We report here that the mapping of single stranded DNA in vivo with potassium permanganate (KMnO4) and nuclear run-on transcription assays reveal that polymerase is paused near position +30 relative to the major c-myc transcription initiation site. Deletion of 350 bp, including the sites of 3'-end formation and intrinsic termination defined in oocyte injection and in vitro transcription assays does not affect-the pausing of polymerase in the promoter-proximal region. In addition, sequences upstream of +47 are sufficient to confer the promoter-proximal pausing of polymerases and to generate the polarity of transcription farther downstream. Thus, the promoter-proximal pausing of RNA polymerase II complexes accounts for the block to elongation within the c-myc gene in mammalian cells. We speculate that modification of polymerase complexes at the promoter-proximal pause site may determine whether polymerases can read through intrinsic sites of termination farther downstream.
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PMID:The block to transcriptional elongation within the human c-myc gene is determined in the promoter-proximal region. 142 80

Assuming that when transcription starts at the P2 promoter of the c-myc gene sites located immediately upstream from P2 are occupied whereas in the absence of initiation they are not, the polymerase chain reaction (PCR)-based method of Mueller & Wold [(1989). Science, 246, 780-786] was used to map in vivo footprints upstream from the P2 promoter in various mouse cell lines. In cultured Friend erythroleukemic cells induced to differentiate with dimethysulfoxide (DMSO), a clear protection corresponding to ME1a2 and E2F sites was observed, consistent with in vitro band-shift and footprint data. However, in cell lines in which the gene was either silent or truncated the footprints were no longer visible. Friend c-myc transcripts decreased to a barely detectable level after 3 h of DMSO treatment. Transcription, as measured by in vitro run-on, was turned off at the level of RNA polymerase elongation rather than initiation [Mechti N., Piechaczyk, M. Blanchard, J.-M., Marty, L., Bonnieu, A., Jeanteur, Ph. & Lebler, B. (1986). Nucleic Acids Res., 24, 9653-9666]. The state of occupancy of the sites did not vary from the first hours up to 9 days of DMSO treatment, suggesting that DNA occupancy per se cannot explain premature termination, which rather would involve a more complex phenomenon.
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PMID:In vivo footprints between the murine c-myc P1 and P2 promoters. 150 92

Premature termination of transcription is assumed to be an important mechanism of c-myc regulation. Induction of terminal differentiation in the promyelocytic leukemia cell line HL60 by dimethyl-sulfoxide (DMSO) is accompanied by a block of RNA elongation within the first exon of the c-myc gene. We have studied the 3'-structure of incompletely elongated transcripts in (i) nuclear RNA of induced and uninduced HL60 cells, (ii) nuclear run-on RNA, and (iii) RNA of in vitro transcribed c-myc constructs. Elongation of c-myc RNA stopped in all three transcriptional systems at similar sites distributed 150-350 bases downstream of the P2 promoter. When HL60 cells were induced to terminal differentiation the short c-myc exon 1 specific RNAs disappeared in nuclear RNA. This implied that RNA polymerase II (pol II) does not continue to transcribe c-myc exon 1 in induced HL60 cells as suggested by earlier nuclear run-on experiments. Therefore, kinetic experiments with small oligonucleotides as probes were performed to determine the start position of pol II on c-myc exon 1 in nuclear run-ons. The results demonstrate that all RNA polymerases are localized at the c-myc P2 promoter in DMSO-treated HL60 cells. Preparation of nuclei for run-on experiments induces a release of pol II from the c-myc P2 promoter leading to the strong nuclear run-on signal on c-myc exon 1. Thus, down-regulation of c-myc in differentiating HL60 cells occurs by retention of pol II at the transcription start site.
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PMID:Hold back of RNA polymerase II at the transcription start site mediates down-regulation of c-myc in vivo. 150 20

Mithramycin is a DNA-binding antibiotic that has been reported to selectively affect c-myc expression [Snyder, R. C. et al., (1991) Biochemistry 30, 4290-4297]. We used in vitro transcription to investigate the specificity of mithramycin action. We found that mithramycin inhibited transcription from the human c-myc P1 and P2 promoters, as well as from a minimal adenovirus-2 major late promoter, with equal efficiencies. Mithramycin also inhibited transcription elongation by creating kinetic blockades to the passage of RNA polymerase II. These data suggest that mithramycin may inhibit transcription non-specifically by affecting general processes such as transcription elongation.
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PMID:In vitro inhibition of c-myc transcription by mithramycin. 153 93

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.
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PMID:A protein-binding site in the c-myc promoter functions as a terminator of RNA polymerase II transcription. 164 97

The term vitamin D includes various chemical species. Vitamin D3 a true endogenous or alimentary prohormone is converted into its main metabolite, calcitriol, by successive hydroxylations in the liver in position 25 and in the kidney in position 1, the production of which is controlled by several factors including parathyroid hormone, blood calcium and phosphorus or insulin as well as by the metabolites of the hormone itself. It controls the synthesis of numerous peptides by acting on gene expression. Indeed, several structural proteins are involved including procollagen alpha 1l, core protein of proteoglycans, diverse regulatory peptides such as protooncogene c-myc and growth factors, "Tumor Necrosis Factor or TNF" and "Nerve Growth Factor or NGF" or hormones such as parathyroid hormone, and finally constitutive proteins of the mineralized tissues such as osteonectin, osteocalcin, osteopontin and calbindins. Therefore, it modulates very different cellular processes. It acts via a nuclear receptor the structure and function of which have been investigated by genetic engineering (cloning of genes encoding for the receptor and hormono-dependent peptides, transfection assays, directed mutagenesis). Actual studies investigate its role in the formation of the complex for transcription initiation near ADN sites, the "Vitamin D Responsive Element or VDRE", located upstream vitamin D-responsive genes and approximately RNA polymerase II. The receptor, which is present in many cell types at various concentrations, would determine spatial and temporal patterns of calcitriol action during development in conjunction with chromatin factors.
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PMID:[Vitamin D: biosynthesis, metabolism and mechanism of action at the cellular level]. 164 84

We have demonstrated, using a combination of nuclear run-off and poly(A) site competition assays, that transcriptional termination occurs between the closely spaced human complement genes, C2 and Factor B, soon after the C2 poly(A) site. A comparison of the C2 termination signal with a functionally similar sequence downstream of the human alpha 2 globin gene reveals that both signals function in an orientation dependent manner, with subfragments of the whole signal displaying partial effects. In the case of the C2 termination sequence a protein binds within it, and is partially responsible for the termination effect. We further demonstrate that the same (or closely related) protein binds to the ME1a1 site in the murine c-myc promoter, which has been implicated in c-myc attenuation. We suggest that the termination/pause sequences positioned downstream of a gene's poly(A) site may constitute the general signals that elicit transcriptional termination in genes transcribed by RNA polymerase II.
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PMID:Transcriptional termination between the closely linked human complement genes C2 and factor B: common termination factor for C2 and c-myc? 175 27

The c-myc promoter has the unusual property of displaying both RNA polymerase II (Pol II) and RNA polymerase III (Pol III) activities. Both Pol II and Pol III utilize the same transcription initiation site. We have now examined the effects of mutations in crucial regions of the c-myc promoter to assess their effects on both transcriptional activities. In doing this we show that both Pol II and Pol III activities require sequences that are located within the stronger of the two principal c-myc promoter regions (P2). Further, we show that the Pol III activity using this initiation site does not require an A box or distal upstream sequences. Like the Pol II activity, it does require an intact TATA sequence and alterations at this site result in the simultaneous loss of both Pol II and Pol III activities. The superimposition of two apparently inseparable promoter activities makes it possible to consider common features, possible common protein elements in each holoenzyme complex, as well as a potential role for each enzyme in the regulated expression of the c-myc gene.
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PMID:In vitro and in vivo analysis of the c-myc RNA polymerase III promoter. 192 71

We have investigated conditions that allow multiple rounds of transcription initiation from the adenovirus major late promoter in an in vitro system derived from HeLa cell nuclear extracts. Templates containing guanine-free cassettes provided a direct assay for discriminating between reinitiated transcripts and transcripts generated by a first-round of transcription initiations. When reactions were reconstituted with the previously characterized class II transcription factors (TFIIA, TFIIB, TFIID, TFIIE/F), transcription by human RNA polymerase II from the adenovirus major late promoter was essentially restricted to a single round of initiations. Reinitiations at previously transcribed major late templates required an additional activity, designated reinitiation transcription factor (RTF). The RTF activity could be separated from the required transcription initiation factors. Semipurified human RTF also promoted transcription reinitiations at minimal promoters derived from the human c-myc, histone H4, and heat shock 70-kDa protein genes, indicating that the same reinitiation factor may be utilized by many, if not all, genes. The possible role of RTF in regulating the transcription rate of various class II genes is discussed.
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PMID:Transcription factor requirement for multiple rounds of initiation by human RNA polymerase II. 196 36


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