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Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Transcription by RNA polymerase I (pol I), pol II, and pol III requires the TATA-binding protein (TBP). This protein functions in association with distinct TBP-associated factors (TAFs) which may specify the nature of the polymerase selected for initiation at a promoter site. In the pol III transcription system, the TBP-TAF complex is a component of the TFIIIB factor. This factor has been resolved into a TBP-TAF complex and another component, both of which are required for reconstitution of transcription by pol III. Neither the TBP-TAF complexes B-TFIID and D-TFIID, which were previously characterized as active for pol II transcription, nor TBP alone can complement pol III transcription reactions that are dependent upon the TBP-TAF subcomponent of TFIIIB. Surprisingly, the TBP-TAF subcomponent of TFIIIB is active in reconstitution of pol II transcription.
Mol Cell Biol 1993 Dec
PMID:TATA-binding protein and associated factors in polymerase II and polymerase III transcription. 824 10

Two copies of nonmobile retrotransposon localized in D. melanogaster heterochromatin (mdg1het) were sequenced at the 3'-end. The comparison of 2.5-kb mdg1het sequences with the sequence of cognate euchomatic transposable copies (mdg1tr) revealed an intact mdg1 ORF2 encoding the pol gene in mdg1het, and two-thirds of nucleotide substitutions in this ORF were synonymous. All the known mdg1 regulatory elements in the mdg1het LTR also are conserved, in spite of numerous deletions and nucleotide substitutions elsewhere in this region. These data suggest that the mdg1het subfamily lost its mobility more recently than other functions were lost. The G-->A hypermutation known to occur in the reverse transcription cycle of retroviruses was detected in one mdg1het copy. The structure of the enchancer-like region in mdg1het suggests a reduced transcription level and, therefore, transposition frequency, relative to mdg1tr. The number of nucleotide substitutions suggests that the time of mdg1het mobility loss was less than 0.3-0.5 Myr ago.
J Mol Evol 1993 Nov
PMID:Two subfamilies of MDG1 retrotransposon with different evolutionary histories in D. melanogaster. 828 81

Several recent studies reported the detection of partially deleted HTLV-I provirus in biopsies of lesions from patients with mycosis fungoides (MF) and T-cell anaplastic large-cell lymphoma. We studied lesions from 59 patients (21 B-cell lymphomas: 16 diffuse and five follicular; 11 cutaneous T-cell lymphomas, including seven MF; one T-immunoblastic lymphoma; 10 diffuse anaplastic large-cell lymphomas: two B, four T, and four of indeterminate phenotype; three Hodgkin's lymphomas; eight atypical lymphoid proliferations; four other lymphoid lesions, and one squamous-cell carcinoma) using primers to the gag, pol and pX regions of HTLV-I in the polymerase chain reaction (PCR) to detect relevant sequences. A total of 10 patients showed one or more PCR-amplifiable products, including five of 11 patients with cutaneous T-cell lymphomas (45%) as compared with one of 21 patients with B-cell lymphomas (4.3%). We did not find a high incidence of positivity in anaplastic large-cell lymphomas, as reported previously. Detectable HTLV-I sequences were not limited to any subtype of lymphoma, and a pX sequence was detected in a squamous-cell carcinoma. Sequence analysis of one amplified product from each of the three regions studied showed a 94.2, 100, and 98.9% homology to the corresponding prototypical gag, pol, and pX HTLV-I sequences, respectively, indicating that the amplified sequences were derived from HTLV-I or a very closely related virus. HTLV-I sequences were detected in a significant proportion of patients with cutaneous T-cell lymphoma, but their role in the pathogenesis of the neoplasm is still unclear.
Diagn Mol Pathol 1993 Sep
PMID:HTLV-I sequence in lymphoproliferative disorders. 828 32

Eukaryotic genomes frequently contain large numbers of repetitive RNA polymerase III (pol III) promoter elements interspersed between and within RNA pol II transcription units, and in several instances a regulatory relationship between the two types of promoter has been postulated. In the budding yeast Saccharomyces cerevisiae, tRNA genes are the only known interspersed pol III promoter-containing repetitive elements, and we find that they strongly inhibit transcription from adjacent pol II promoters in vivo. This inhibition requires active transcription of the upstream tRNA gene but is independent of its orientation and appears not to involve simple steric blockage of the pol II upstream activator sites. Evidence is presented that different pol II promoters can be repressed by different tRNA genes placed upstream at varied distances in both orientations. To test whether this phenomenon functions in naturally occurring instances in which tRNA genes and pol II promoters are juxtaposed, we examined the sigma and Ty3 elements. This class of retrotransposons is always found integrated immediately upstream of different tRNA genes. Weakening tRNA gene transcription by means of a temperature-sensitive mutation in RNA pol III increases the pheromone-inducible expression of sigma and Ty3 elements up to 60-fold.
Mol Cell Biol 1994 Feb
PMID:tRNA genes as transcriptional repressor elements. 828 6

RNA chain elongation by RNA polymerase is a dynamic process. Techniques that allow the isolation of active elongation complexes have enabled investigators to describe individual steps in the polymerization of RNA chains. This article will describe recent studies of elongation by RNA polymerase II (pol II). At least four types of blockage to chain elongation can be overcome by elongation factor SII: (a) naturally occurring "arrest" sequences, (b) DNA-bound protein, (c) drugs bound in the DNA minor groove, and (d) chain-terminating substrates incorporated into the RNA chain. SII binds to RNA polymerase II and stimulates a ribonuclease activity that shortens nascent transcripts from their 3' ends. This RNA cleavage is required for chain elongation from some template positions. As a result, the pol II elongation complex can repeatedly shorten and reextend the nascent RNA chain in a process we refer to as cleavage-resynthesis. Hence, assembly of large RNAs does not necessarily proceed in a direct manner. The ability to shorten and reextend nascent RNAs means that a transcription impediment through which only half the enzyme molecules can proceed per encounter, can be overcome by 99% of the molecules after six iterations of cleavage-resynthesis. Surprisingly, the boundaries of the elongation complex do not move upstream after RNA cleavage. The physico-chemical alterations in the elongation complex that accompany RNA cleavage and permit renewed chain elongation are not yet understood.
Cell Mol Biol Res 1993
PMID:Transcription elongation by RNA polymerase II: mechanism of SII activation. 831 68

RNA polymerase II (pol II) transcription complexes initiated from the adenovirus major late promoter can become blocked both in vitro and in vivo at a specific site within the first intron of the transcription unit. In vitro, polymerases that fail to read through the major late attenuation site remain stably bound to the template in a ternary complex that is indefinitely blocked from continuing elongation, a phenomenon referred to as "arrest." Elongation factor SII has been shown both to promote readthrough of this and other arrest sites and to stimulate a previously unknown 3' to 5' exonuclease activity of pol II. We have proposed that the two activities are related and that SII promotes readthrough by means of the enhancement of the exonuclease activity. In the experiments reported here, we have tested several features of that model. In particular, we have examined the hypothesis that SII stimulates readthrough by allowing the polymerase to undergo multiple cycles of removal and resynthesis of RNA bases preceding the attenuation site. In addition, we present experimental support for the proposal that the length of time polymerase pauses at the attenuation site is important to the efficiency of arrest. The results of these experiments are discussed in the context of the model.
Cell Mol Biol Res 1993
PMID:Transcriptional pausing, arrest, and readthrough at the adenovirus major late attenuation site. 831 69

HMG boxes were initially identified as DNA-binding domains of the human RNA polymerase I (pol I) transcription factor hUBF and the animal high-mobility-group (HMG) protein family HMG1. Since then, numerous sequences of HMG-box-containing HMG proteins and other DNA-binding proteins from several species have become available. By sequence comparisons of a selected range of HMG boxes from these proteins and the construction of phylogenetic trees we show that the HMG box is highly conserved between DNA-binding proteins of organisms from all three eukaryotic kingdoms and that HMG boxes are linked by distinct evolutionary relationships. In addition, most HMG boxes display comparable hydropathy profiles and amino acid arrangements, which could serve as nuclear targeting sequences.
J Mol Evol 1993 Aug
PMID:Phylogenetic relationships of HMG box DNA-binding domains. 841 Dec 10

We have investigated the expression of two Schizosaccharomyces pombe replicative DNA polymerases alpha and delta during the cell cycle. The pol alpha+ and pol delta+ genes encoding DNA polymerases alpha and delta were isolated from S. pombe. Both pol alpha+ and pol delta+ genes are single copy genes in haploid cells and are essential for cell viability. In contrast to Saccharomyces cerevisiae homologs, the steady-state transcripts of both S. pombe pol alpha+ and pol delta+ genes were present throughout the cell cycle. Sequence analysis of the pol alpha+ and pol delta+ genes did not reveal the Mlu I motifs in their upstream sequences that are involved in cell cycle-dependent transcription of S. cerevisiae DNA synthesis genes as well as the S. pombe cdc22+ gene at the G1/S boundary. However, five near-match Mlu I motifs were found in the upstream region of the pol alpha+ gene. S. pombe DNA polymerases alpha and delta proteins were also expressed constantly throughout the cell cycle. In addition, the enzymatic activity of the S. pombe DNA polymerase alpha measured by in vitro assay was detected at all stages of the cell cycle. Thus, these S. pombe replicative DNA polymerases, like that of S. pombe cdc17+ gene, are expressed throughout the cell cycle at the transcriptional and protein level. These results indicate that S. pombe has at least two regulatory modes for the expression of genes involved in DNA replication and DNA precursor synthesis.
Mol Biol Cell 1993 Feb
PMID:Cell cycle expression of two replicative DNA polymerases alpha and delta from Schizosaccharomyces pombe. 844 13

The first exon of the human c-myc gene can be transcribed by either RNA polymerase II or RNA polymerase III. The molecular factors contributing to polymerase selection are not yet completely defined. We have examined the role of chromatin structure in regulating transcription by RNA polymerase III. Using as competitor a pol III gene in both a cis and trans arrangement, we demonstrate that c-myc gene expression is facilitated from templates containing a minimal number of fully assembled nucleosomes. The removal of excess histones by DNA titration leads to an elevated level of c-myc expression. These results suggest that either the c-myc expression is inhibited when the template is fully packaged into chromatin or that the affinity of RNA polymerase for the regulatory elements of this exon is such that a template, devoid of histones, is required for transcriptional initiation.
Mol Cell Biochem 1993 Mar 10
PMID:In vitro transcription of the c-myc first exon may be influenced by the extent of chromatin assembly. 845 2

The 130-bp repetitive element (RE) of the rat rDNA (ribosomal RNA-encoding gene) intergenic spacer stimulated the synthesis of rRNA four- to sixfold, in comparison with that of the promoter alone, both in vivo and in vitro, when ligated to the rat rDNA promoter. The addition of increasing amounts of highly purified E1BF (enhancer-1 binding factor), which binds to the rat rDNA promoter and an upstream nonrepetitive enhancer element [Zhang and Jacob, Mol. Cell. Biol. 10 (1990) 5177-5186], to an in vitro transcription system resulted in enhancement of rDNA transcription from the recombinant plasmids containing the promoter or promoter-RE. However, E1BF-mediated stimulation of transcription under the influence of the RE continued at higher concentrations of E1BF than did the control transcription from the promoter alone. The binding affinity of E1BF for the RE was comparable to its affinity for the nonrepetitive far upstream enhancer element previously characterized in our laboratory. The sequences protected by E1BF in the RE differed from those protected by UBF (upstream control element-binding factor), a well characterized pol I transcription factor. These data suggest that E1BF belongs to a class of transcription factors which interact with the promoter and spacer cis-acting RE to modulate rDNA transcription.
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PMID:Characterization of the 130-bp repeat enhancer element of the rat ribosomal gene: functional interaction with transcription factor E1BF. 846 76


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