Characterization of tRNACys processing in a conditional Bacillus subtilis CCase mutant reveals the participation of RNase R in its quality control

Abstract

We generated a conditional CCase mutant ofBacillus subtilisto explore the participationin vivoof the tRNA nucleotidyltransferase (CCA transferase or CCase) in the maturation of the single-copy tRNACys, which lacks an encoded CCA 3′ end. We observed that shorter tRNACysspecies, presumably lacking CCA, only accumulated when the inducible Pspac : ccawas introduced into anrnrmutant strain, but not in combination withpnp. We sequenced the tRNA 3′ ends produced in the various mutant tRNACysspecies to detect maturation and decay intermediates and observed that decay of the tRNACysoccurs through the addition of poly(A) or heteropolymeric tails. A few clones corresponding to full-size tRNAs contained either CCA or other C and/or A sequences, suggesting that these are substrates for repair and/or decay. We also observed editing of tRNACysat position 21, which seems to occur preferentially in mature tRNAs. Altogether, our results providein vivoevidence for the participation of theB. subtilis ccagene product in the maturation of tRNAs lacking CCA. We also suggest that RNase R exoRNase inB. subtilisparticipates in the quality control of tRNA.