Endonucleolytic processing of CCA-less tRNA precursors by RNase Z in Bacillus subtilis

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Abstract
In contrast to Escherichia coli , where the 3′ ends of tRNAs are primarily generated by exoribonucleases, maturation of the 3′ end of tRNAs is catalysed by an endoribonuclease, known as RNase Z (or 3′ tRNase), in many eukaryotic and archaeal systems. RNase Z cleaves tRNA precursors 3′ to the discriminator base. Here we show that this activity, previously unsuspected in bacteria, is encoded by the yqjK gene of Bacillus subtilis . Decreased yqjK expression leads to an accumulation of a population of B.subtilis tRNAs in vivo , none of which have a CCA motif encoded in their genes, and YqjK cleaves tRNA precursors with the same specificity as plant RNase Z in vitro . We have thus renamed the gene rnz . A CCA motif downstream of the discriminator base inhibits RNase Z activity in vitro , with most of the inhibition due to the first C residue. Lastly, tRNAs with long 5′ extensions are poor substrates for cleavage, suggesting that for some tRNAs, processing of the 5′ end by RNase P may have to precede RNase Z cleavage.