PubMed:821947 JSONTXT

{"project":"sentences","denotations":[{"id":"T1","span":{"begin":0,"end":96},"obj":"Sentence"},{"id":"T2","span":{"begin":97,"end":209},"obj":"Sentence"},{"id":"T3","span":{"begin":210,"end":379},"obj":"Sentence"},{"id":"T4","span":{"begin":380,"end":523},"obj":"Sentence"},{"id":"T5","span":{"begin":524,"end":738},"obj":"Sentence"},{"id":"T6","span":{"begin":739,"end":950},"obj":"Sentence"},{"id":"T7","span":{"begin":951,"end":1124},"obj":"Sentence"},{"id":"T8","span":{"begin":1125,"end":1325},"obj":"Sentence"},{"id":"T9","span":{"begin":1326,"end":1440},"obj":"Sentence"},{"id":"T10","span":{"begin":1441,"end":1524},"obj":"Sentence"},{"id":"T1","span":{"begin":0,"end":96},"obj":"Sentence"},{"id":"T2","span":{"begin":97,"end":209},"obj":"Sentence"},{"id":"T3","span":{"begin":210,"end":379},"obj":"Sentence"},{"id":"T4","span":{"begin":380,"end":523},"obj":"Sentence"},{"id":"T5","span":{"begin":524,"end":738},"obj":"Sentence"},{"id":"T6","span":{"begin":739,"end":950},"obj":"Sentence"},{"id":"T7","span":{"begin":951,"end":1124},"obj":"Sentence"},{"id":"T8","span":{"begin":1125,"end":1325},"obj":"Sentence"},{"id":"T9","span":{"begin":1326,"end":1440},"obj":"Sentence"},{"id":"T10","span":{"begin":1441,"end":1524},"obj":"Sentence"}],"namespaces":[{"prefix":"_base","uri":"http://pubannotation.org/ontology/tao.owl#"}],"text":"Mechanism of formation of reovirus mRNA 5'-terminal blocked and methylated sequence, m7GpppGmpC.\nBlocked and methylated 5' termini of reovirus mRNA are formed by viral cores at an early stage of transcription. Cores incubated in a complete transcription reaction mixture for 30 s, or in a mixture lacking UTP and ATP for a longer time, synthesize the \"cap\" structure, m7GpppGmpC. The dinucleotide ppGpC functions as substrate for a core-associated guanylyltransferase and is converted to GpppGpC by addition of pG from GTP. For optimal conversion, both the diphosphate terminus and phosphodiester bond are required. pGpC is not a substrate, but pppGpC is utilized after removal of the gamma-phosphate by a core nucleotide phospohydrolase. Methyltransferases also present in cores transfer methyl groups sequentially from S-adenosylmethionine (AdoMet) to the N7-position of the 5'-terminal guanosine followed by the 2'-OH of the penultimate guanosine. GpppGpC is hydrolyzed by cores in the presence of pyrophosphate to ppGpC, the predominant 5'-terminal structure of reovirus mRNA made in the absence of S-adenosylmethionine. N7-methylation prevents pyrophosphorolysis of m7GpppGpC, which may explain the increased proportion of blocked, methylated 5' termini in viral mRNA synthesized in the presence of S-adenosylmethionine. On the basis of these findings, the following reaction series is proposed for the synthesis of reovirus mRNA caps. In the series, AdoHcy is the abbreviation for S-adenosylhomocysteine (see article)9"}