title: Initiation of reovirus transcription by inosine 5'-triphosphate and properties of 7-methylinosine-capped, inosine-substituted messenger ribonucleic acids.
abstract: Inosine 5'-triphosphate (ITP) can be utilized in place of guanosine 5'-triphosphate (GTP) for both the initiation and the elongation steps of reovirus transcription, resulting in the synthesis of mRNAs containing 5'-terminal m7IpppIm and internal pI. The apparent molecular weights of the I-substituted products were altered as a consequence of the absence of G-C base pairs and accompanying loss of ordered structure. The migration of I-substituted RNAs in agarose gels and glycerol gradients was similar to glyoxal-treated transcripts; i.e., it decreased 2-fold as compared to the corresponding untreated G-containing mRNAs. 7-Methylinosine-capped (m7I-capped), I-substituted transcripts readily attached to wheat germ 80S ribosomes. Unlike native G-containing mRNAs, they also formed heavier complexes that sedimented faster than 80S complexes even in the presence of the nonhydrolyzable ATP analogue AMPP(NH)P and elongation inhibitor sparsomycin. I-substituted molecules that were capped posttranscriptionally to form m7G-capped 5' ends yielded mostly 80S monosomes, consistent with a strong influence of 5'-terminal structure on initiation of translation. Under limited conditions of initiation, I-substituted RNAs outcompeted G-containing transcripts for ribosome attachment. Although the results are consistent with enhanced binding and freer movement of ribosomes on unstructured templates, synthesis of acid-precipitable polypeptides in wheat germ extract directed by I-substituted RNAs was 15-fold less than with G-containing mRNAs.
mesh_terms: D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D007292:Inosine Nucleotides / Q000378:metabolism*; D007293:Inosine Triphosphate / Q000378:metabolism*; D012089:Mammalian orthoreovirus 3 / Q000378:metabolism*; D008970:Molecular Weight; D012314:RNA Cap Analogs / Q000378:metabolism*; D012315:RNA Caps / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism*; D012335:RNA, Ribosomal / Q000378:metabolism; D012367:RNA, Viral / Q000378:metabolism*; D012087:Reoviridae / Q000378:metabolism*; D014158:Transcription, Genetic; D014908:Triticum / Q000378:metabolism
chemical_list: D007292:Inosine Nucleotides; D012314:RNA Cap Analogs; D012315:RNA Caps; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D012367:RNA, Viral; D007293:Inosine Triphosphate