title: Mechanism of formation of reovirus mRNA 5'-terminal blocked and methylated sequence, m7GpppGmpC.
abstract: Blocked 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
mesh_terms: D004492:Edetic Acid / Q000494:pharmacology; D004789:Enzyme Activation; D008274:Magnesium / Q000494:pharmacology; D009841:Oligonucleotides / Q000378:metabolism*; D009843:Oligoribonucleotides / Q000032:analysis / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis*; D012087:Reoviridae / Q000187:drug effects / Q000378:metabolism*; D012359:tRNA Methyltransferases / Q000378:metabolism
chemical_list: D009841:Oligonucleotides; D009843:Oligoribonucleotides; D012333:RNA, Messenger; D004492:Edetic Acid; D012359:tRNA Methyltransferases; D008274:Magnesium