Growth rate-dependent regulation of transfer ribonucleic acid (5-methyluridine) methyltransferase in Escherichia coli B/r.

Enzymes catalyzing the transfer of methyl groups from S-adenosyl-l-methionine to a precursor transfer ribonucleic acid (tRNA) and forming 5-methyluridine (m(5)U), 1-methylguanine (m(1)G), or 5-methylaminomethyl-2-thio-uridine (mam(5)s(2)U) are denoted tRNA(m(5)U)-(EC 2.1.1.35), tRNA(m(1)G)-(EC 2.1.1.31), and tRNA(mam(5)s(2)U)methyltransferase. We have studied the regulation of these tRNA biosynthetic enzymes in Escherichia coli under various physiological conditions and in bacterial mutants known to affect the regulation of components of the translational apparatus. Such studies have revealed that tRNA(m(5)U)-methyltransferase increases with the growth rate in the same fashion as stable RNA, whereas the activity of two other tRNA methyltransferases remains constant in relation to the growth rate. Thus, these tRNA biosynthetic enzymes were not coordinately regulated. Regulation of both tRNA(m(5)U)methyltransferase and stable RNA was similar during shift-up and shift-down experiments. This enzyme showed a stringent regulation in relA(+) strain (T. Ny and G. R. Björk, J. Bacteriol. 130:635-641, 1977) but also in two temperature-sensitive mutants, fusA and fusB, known to influence the accumulation of guanosine 5'-diphosphate 3'-diphosphate and RNA synthesis at nonpermissive temperatures. The tRNA(m(5)U)methyltransferase showed a gene dose effect when its structural gene, trmA, was carried on a plasmid or on lambda transducing phages. Although the regulation of tRNA-(m(5)U)methyltransferase was surprisingly coupled to that of stable RNA, this enzyme was expressed at a much lower level.