Open Access“Pretranscriptional capping” in the biosynthesis of cytoplasmic polyhedrosis virus mRNA
Author(s) -
Yasuhiro Furuichi
Publication year - 1978
Publication title -
proceedings of the national academy of sciences of the united states of america
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.011
H-Index - 771
eISSN - 1091-6490
pISSN - 0027-8424
DOI - 10.1073/pnas.75.3.1086
Subject(s) - messenger rna , nucleotide , biosynthesis , transcription (linguistics) , rna , biology , microbiology and biotechnology , nucleoside , biochemistry , methylation , cytoplasm , enzyme , chemistry , gene , linguistics , philosophy
Thein vitro synthesis of cytoplasmic polyhedrosis virus (CPV) mRNA was previously shown to be dependent upon the presence of the methyl donorS -adenosylmethionine (AdoMet). We now find that the competitive inhibitor of methylation,S -adenosylhomocysteine (AdoHcy), also stimulates CPV mRNA synthesis efficiently, resulting in the synthesis of viral mRNAs containing 5′-terminal GpppA and ppA, rather than m7 GpppAm as observed with Adomet. In addition to AdoHcy, other AdoMet analogues, includingS -adenosylethionine and adenosine, also stimulate CPV mRNA synthesis but to a smaller extent than does AdoHcy or AdoMet. In order to study the relationship between cap formation and mRNA synthesis, nucleoside triphosphates were replaced in the RNA-synthesizing reaction mixture (containing AdoMet) by the corresponding β,γ-imido analogues, which are resistant to nucleotide phosphohydrolase, an enzyme involved in cap formation. Although mRNA synthesis occurred in the presence of UMP-pNHp or GMP-pNHp, none was observed when AMP-pNHp was substituted for ATP. Because the ATP molecule that becomes the 5′-terminal nucleotide of CPV mRNA must be cleaved at the β-γ position during cap formation, the results suggest that, in this viral transcription system, cap formation is prerequisite to mRNA synthesis—i.e., a “pretranscriptional” event.