Stationary-phase expression and aminoacylation of a transfer-RNA-like small RNA

Genome‐scale analyses have shown numerous functional duplications in the canonical translational machinery. One of the most striking examples is the occurrence of unrelated class I and class II lysyl‐transfer RNA synthetases (LysRS), which together may aminoacylate non‐canonical tRNAs. We show that, in Bacillus cereus , the two LysRSs together aminoacylate a small RNA of unknown function named tRNA Other , and that the aminoacylated product stably binds translation elongation factor Tu. In vitro reconstitution of a defined lysylation system showed that Lys‐tRNA Other is synthesized in the presence of both LysRSs, but not by either alone. In vivo analyses showed that the class 2 LysRS was present both during and after exponential growth, whereas the class I enzyme and tRNA Other were predominantly produced during the stationary phase. Aminoacylation of tRNA Other was also found to be confined to the stationary phase, which suggests a role for this non‐canonical tRNA in growth‐phase‐specific protein synthesis.