Two Species of Bacillus subtilis Tyrosine Transfer Ribonucleic Acid

The ratio of two species of tyrosine acceptor transfer RNA, tRNAtyri and tRNAtyrii, changes dramatically during growth of Bacillus subtilis W168 in various media. Tyrosyl-tRNAi and tyrosyl-tRNAii, as well as tRNAtyri and tRNAtyrii, are resolved by methylated albumin-Kieselguhr chromatography. The alteration may be due to selective transcription of structural genes or by subsequent modification of one species of tRNAtyr. Methods used to effect interconversion of tRNAtyri and tRNAtyrii in vitro were not successful. Both species of tRNAtyr are recognized by the same aminoacyltRNA synthetase and are acylated and deacylated (enzymatically or nonenzymatically) at similar rates. Both species transfer tyrosine into polypeptides in response to poly (U2, A) and poly (U, A, C) in the Escherichia coli S-30 system and exhibit similar magnesium optima for transfer in vitro of tyrosine into polypeptides. Differential usage of tyrosyl-tRNAi and tyrosyl-tRNAii in vivo seems unlikely because the ratio of the two species bound to polysomes reflects their ratio in bulk tRNA. The possibility that biological significance could be ascribed to the alteration of the relative amounts of tRNAtyri and tRNAtyrii has not been completely eliminated; nevertheless, it was not apparent in this study.