Transfer RNA(5-methylaminomethyl-2-thiouridine)-methyltransferase from Escherichia coli K-12 has two enzymatic activities.

摘要: The tRNA(5-methylaminomethyl-2-thiouridine)-methyltransferase, which is involved in the biosynthesis of modified nucleoside 5-methylaminomethyl-2-thiouridine (mnm5s2U) present wobble position some tRNAs, was purified close to homogeneity (95% purity). molecular mass enzyme 79,000 daltons. activity has a pH optimum 8.0-8.5, inhibited by magnesium ions, and stimulated ammonium ions. Two different intermediates mnm5s2U34 are tRNA from mutants trmC1 trmC2. Unexpectedly, product cells identified spectrometric chromatographic analyses as 5-carboxymethylaminomethyl-2-thiouridine (cmnm5s2U), i.e. more complex derivative than final mnm5s2U. trmC2 5-aminomethyl-2-thiouridine (nm5s2U). In presence S-adenosylmethionine most fraction converts both cmnm5s2U34 nm5s2U34 into mnm5s2U34. absence S-adenosylmethionine, however, converted nm5s2U this fraction. We conclude that polypeptide two enzymatic activities; one actually demodifies cmnm5s2U other catalyzes transfer methyl group nm5s2U, thus forming sequential order suggested be: (Formula: see text). methyltransferase (nm5s2U34----mnm5s2U34) 74 min-1, steady state concentration only 78 molecules/genome equivalent growing at specific growth rate 1.0/h.