The coding properties of methyl-deficient leucyl-transfer RNA.

Escherichia coli 58-161, a methionine auxotroph with "relaxed control", synthesizes methyl-deficient transfer RNA (tRNA) when subjected to methionine deprivation. Whereas [14C]leucyl-tRNA from normally grown bacteria fractionates into two peaks (I and II) on methylated albumin-kieselguhr columns, methyl-deficient [14C]leucyl-tRNA shows an additional component (peak III). A ribosome-binding assay shows a marked difference in the coding response to poly UC and poly UG between normal and methyl-deficient [14C]leucyl-tRNA. Compared to normal E. coli 58-161 [14C]leucyl-tRNA, the leucine-tRNA isolated from methionine-deprived cells, manifests a twofold increase in poly UG response and a fivefold increase in poly UC response. Chromatography on methylated albumin-kieselguhr columns localized the increase in poly UG reactive tRNA to peak II. The chromatographic component of leucyl-tRNA characteristic of methyl-deficiency (peak III) responded exclusively to poly UC. These results are discussed in terms of a possible requirement for methylated bases in tRNA for specific codon recognition.