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.