title: Partial purification and characterization of a ribonucleic acid N2-guanine methyltransferase associated with avian myeloblastosis virus.
abstract: A nucleic acid methylase, N2-guanine ribonucleic acid (RNA) methyltransferase, which is associated with type C RNA tumor viruses, has been purified from avian myeloblastosis virions by gel filtration on Sephadex G-200, followed by chromatography on hydroxylapatite. The molecular weight estimated by gel filtration is 220 000, and the methylase activity has a pH optimum of 7.6--7.9. Magnesium and ammonium ions both stimulate activity 1.5-fold at 9.5 mM and 0.36 M, respectively, but apparently neither is essential for activity. Both daunomycin and adriamycin, antineoplastic drugs, also increase activity 1.5-fold at 1 mM. The enzyme was purified 120-fold from the virions and the activity is partially stabilized by dithiothretiol, but large losses were sustained during 24-h dialysis. The purified enzyme retains 75% of its activity on storage at -25 degrees C for 2 months in buffer containing 50% glycerol. Escherichia coli tRNAPhe and tRNAVal are preferred substrates with methylation occurring at position 10 of E. coli tRNAPhe.
mesh_terms: D001354:Avian Leukosis Virus / Q000201:enzymology*; D009189:Avian Myeloblastosis Virus / Q000201:enzymology*; D003630:Daunorubicin / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology; D004789:Enzyme Activation; D006147:Guanine / Q000031:analogs & derivatives; D007700:Kinetics; D008274:Magnesium / Q000494:pharmacology; D008970:Molecular Weight; D013379:Substrate Specificity; D012359:tRNA Methyltransferases / Q000302:isolation & purification / Q000378:metabolism*
chemical_list: D006147:Guanine; D004317:Doxorubicin; D012359:tRNA Methyltransferases; D008274:Magnesium; D003630:Daunorubicin