RNA-dependent RNA polymerase

About: RNA-dependent RNA polymerase is a research topic. Over the lifetime, 13904 publications have been published within this topic receiving 767954 citations. The topic is also known as: RdRp & RNA replicase.

The 54-kD protein of signal recognition particle contains a methionine-rich RNA binding domain.

Abstract: Signal recognition particle (SRP) plays the key role in targeting secretory proteins to the membrane of the endoplasmic reticulum (Walter, P., and V. R. Lingappa. 1986. Annu. Rev. Cell Biol. 2:499-516). It consists of SRP7S RNA and six proteins. The 54-kD protein of SRP (SRP54) recognizes the signal sequence of nascent polypeptides. The 19-kD protein of SRP (SRP19) binds to SRP7S RNA directly and is required for the binding of SRP54 to the particle. We used deletion mutants of SRP19 and SRP54 and an in vitro assembly assay in the presence of SRP7S RNA to define the regions in both proteins which are required to form a ribonucleoprotein particle. Deletion of the 21 COOH-terminal amino acids of SRP19 does not interfere with its binding to SRP7S RNA. Further deletions abolish SRP19 binding to SRP7S RNA. The COOH-terminal 207 amino acids of SRP54 (M domain) were found to be necessary and sufficient for binding to the SRP19/7S RNA complex in vitro. Limited protease digestion of purified SRP confirmed our results for SRP54 from the in vitro binding assay. The SRP54M domain could also bind to Escherichia coli 4.5S RNA that is homologous to part of SRP7S RNA. We suggest that the methionine-rich COOH terminus of SRP54 is a RNA binding domain and that SRP19 serves to establish a binding site for SRP54 on the SRP7S RNA.

Subunits shared by eukaryotic nuclear RNA polymerases.

Abstract: RNA polymerases I, II, and III share three subunits that are immunologically and biochemically indistinguishable. The Saccharomyces cerevisiae genes that encode these subunits (RPBS, RPB6, and RPBS) were isolated and sequenced, and their transcriptional start sites were deduced. RPB5 encodes a 25-kD protein, RPB6, an 18-kD protein, and RPB8, a 16-kD protein. These genes are single copy, reside on different chromosomes, and are essential for viability. The fact that the genes are single copy, corroborates previous evidence suggesting that each of the common subunits is identical in RNA polymerases I, II, and III. Furthermore, immunoprecipitation of RPB6 coprecipitates proteins whose sizes are consistent with RNA polymerase I, II, and III subunits. Sequence similarity between the yeast RPB5 protein and a previously characterized human RNA polymerase subunit demonstrates that the common subunits of the nuclear RNA polymerases are well conserved among eukaryotes. The presence of these conserved and essential subunits in all three nuclear RNA polymerases and the absence of recognizable sequence motifs for DNA and nucleoside triphosphate-binding indicate that the common subunits do not have a catalytic role but are important for a function shared by the RNA polymerases such as transcriptional efficiency, nuclear localization, enzyme stability, or coordinate regulation of rRNA, mRNA, and tRNA synthesis. .,

Gamma-monomethyl phosphate: a cap structure in spliceosomal U6 small nuclear RNA.

Abstract: U6 small nuclear RNA (snRNA), a component of eukaryotic spliceosomes, is required for splicing of nuclear pre-mRNAs. Whereas trimethylguanosine cap-containing U sn-RNAs are transcribed by RNA polymerase II, the U6 RNA is transcribed by RNA polymerase III and contains a nonnucleotide cap structure on its 5' end. We characterized the cap structure of human U6 snRNA and show that the gamma phosphate of the 5' guanosine triphosphate is methylated. The mobilities of in vivo-modified gamma phosphate from the 5' end of HeLa U6 RNA were identical to the synthetic monomethyl phosphate (CH3-O-P) in two-dimensional chromatography and two-dimensional electrophoresis. The cap structure of U6 RNA is distinct from all other cap structures characterized thus far.

Processing of topoisomerase I cleavable complexes into DNA damage by transcription

Abstract: Topoisomerase I (TOP1)-mediated DNA damage induced by camptothecin (CPT) in the presence of active transcription has been studied using purified calf thymus TOP1 and T7 RNA polymerase. CPT-stabilized TOP1 cleavable complexes located on the template strand within the transcribed region were found to be converted into irreversible strand breaks by the elongating RNA polymerase. By contrast, CPT-stabilized TOP1 cleavable complexes located on the non-template strand within the transcribed region was unaffected by the elongating RNA polymerase. Previous studies have demonstrated that the elongating T7 RNA polymerase is arrested by TOP1 cleavable complexes located on the template but not the non-template strand [Bendixen et al ., (1990) Biochemistry , 29, 5613-5619]. Together, these results suggest a model in which collision between the TOP1-cleavable complexes located on the template strand and the elongating RNA polymerase results in transcription arrest and conversion of TOP1 cleavable complexes into 'irreversible' strand breaks. The implication of the transcription collision model in DNA damage and repair, as well as cell killing, is discussed.