Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: EC:2.7.7.48 (transcriptase)
 9,479 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

It has previously been observed that the only specific requirement for transcriptional initiation on viral RNA in vitro by the RNA-dependent RNA polymerase (RdRp) of turnip yellow mosaic virus is the CCA at the 3' end of the genome. We now compare the abilities of this RdRp, turnip crinkle virus RdRp, and Qbeta replicase, an enzyme capable of supporting the complete viral replication cycle in vitro, to transcribe RNA templates containing multiple CCA boxes but lacking specific viral sequences. Each enzyme is able to initiate transcription from several CCA boxes within these RNAs, and no special reaction conditions are required for these activities. The transcriptional yields produced from templates comprised of multiple CCA or CCCA repeats relative to templates derived from native viral RNA sequences vary between 2:1 and 0.1:1 for the different RdRps. Control of initiation by such redundant sequences presents a challenge to the specificity of viral transcription and replication. We identify 3'-preferential initiation and sensitivity to structural presentation as two specificity mechanisms that can limit initiation among potential CCA initiation sites. These two specificity mechanisms are used to different degrees by the three RdRps. The finding that three viral RdRps representing two of the three supergroups within the positive-strand RNA viral RdRp phylogeny support substantial transcription in the absence of unique promoters suggests that this phenomenon may be common among positive-strand viruses. A framework is presented arguing that replication of viral RNA in the absence of unique promoter elements is feasible.
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PMID:CCA initiation boxes without unique promoter elements support in vitro transcription by three viral RNA-dependent RNA polymerases. 1083 91

UV irradiation of a mixture of an isolated tobacco mosaic virus (TMV; tomato strain L [TMV-L]) RNA-dependent RNA polymerase complex and the TMV-L RNA 3'-terminal region (3'-TR) resulted in cross-linking of the TMV-L 126-kDa replication protein to the TMV-L 3'-TR. Using both Escherichia coli-expressed proteins corresponding to parts of the 126-kDa protein and mutants of the 3'-TR, the interacting sites were located to a 110-amino-acid region just downstream of the core methyltransferase domain in the protein and a region comprising the central core C and domain D2 in the 3'-TR. Mutation to alanine of a tyrosine residue at position 409 or a tyrosine residue at position 416 in the protein binding region abolished cross-linking to the 3'-TR, and corresponding mutations introduced into TMV-L RNA abolished its ability to replicate in tomato protoplasts, with no detectable production of either plus- or minus-strand RNA. The results are compatible with a model for initiation of TMV-L minus-strand RNA synthesis in which an internal region of the TMV-L 126-kDa protein first binds to the central core C and domain D2 region of the TMV-L 3'-TR and is then followed by binding of the 183-kDa protein to this complex and positioning of the catalytically active site of the polymerase domain close to the 3'-terminal CCCA initiation site.
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PMID:Identification of a region of the tobacco mosaic virus 126- and 183-kilodalton replication proteins which binds specifically to the viral 3'-terminal tRNA-like structure. 1288 85