Modification of RNA by mRNA guanylyltransferase and mRNA (guanine-7-)methyltransferase from vaccinia virions.

A purified enzyme system isolated from vaccinia virus cores has been shown to modify the 5' termini of viral mRNA and synthetic poly(A) and poly(G) to form the structures m7G(5')pppA- and m7G(5')pppG-. The enzyme system has both guanylyltransferase and methyltransferase activities. The GTP:mRNA guanylyltransferase activity incorporates GMP into the 5' terminus via a 5'-5' triphosphate bond. The properties of this reaction are: (a) of the four nucleoside triphosphates only GTP is a donor, (b) mRNA with two phosphates at the 5' terminus is an acceptor while RNA with a single 5'-terminal phosphate is not, (c) Mg2+ is required, (d) the pH optimum is 7.8, (e) PP1 is a strong inhibitor, and (f) the reverse reaction, namely the formation of GTP from PP1 and RNA containing the 5'-terminal structure G(5')pppN-, readily occurs. The S-adenosylmethionine:mRNA(guanine-7-)methyltransferase activity catalyzes the methylation of the 5'-terminal guanosine. This reaction exhibits the following characteristics: (a) mRNA with the 5'-terminal sequences G(5')pppA- and G(5')pppG- are acceptors, (b) only position 7 of the terminal guanosine is methylated; internal or conventional 5'-terminal guanosine residues are not methylated, (c) the reaction is not dependent upon GTP or divalent cations, (d) optimal activity is observed in a broad pH range around neutrality, (e) the reaction is inhibited by S-adenosylhomocysteine. Both the guanylyltransferase and methyltransferase reactions exhibit bisubstrate kinetics and proceed via a sequential mechanism. The reactions may be summarized: (see article).
AuthorsS A Martin, B Moss
JournalThe Journal of biological chemistry (J Biol Chem) Vol. 250 Issue 24 Pg. 9330-5 (Dec 25 1975) ISSN: 0021-9258 [Print] UNITED STATES
PMID1194287 (Publication Type: Journal Article)
Chemical References
  • Cations, Divalent
  • Guanine Nucleotides
  • RNA, Messenger
  • Poly A
  • S-Adenosylmethionine
  • S-Adenosylhomocysteine
  • Methyltransferases
  • Nucleotidyltransferases
  • Magnesium
  • Cations, Divalent
  • Guanine Nucleotides
  • Kinetics
  • Magnesium (pharmacology)
  • Methyltransferases (metabolism)
  • Nucleotidyltransferases (metabolism)
  • Poly A
  • RNA, Messenger
  • S-Adenosylhomocysteine (pharmacology)
  • S-Adenosylmethionine (pharmacology)
  • Structure-Activity Relationship
  • Vaccinia virus (enzymology)

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