RNase Y, a novel endoribonuclease, initiates riboswitch turnover in Bacillus subtilis.

In contrast to Escherichia coli, initiation of mRNA decay in Gram-positive organisms is poorly understood. We studied the fate of the highly structured RNAs generated by premature transcription termination of S-adenosylmethionine (SAM)-dependent riboswitches in Bacillus subtilis. An essential protein of earlier unknown function, YmdA, was identified as a novel endoribonuclease (now called RNase Y) that was capable of preferential cleaving in vitro of the 5' monophosphorylated yitJ riboswitch upstream of the SAM-binding aptamer domain. Antiterminated full-length yitJ mRNA was not a substrate for RNase Y in vivo and in vitro, transcripts capable of forming the antiterminator were only cleaved in the presence of SAM. Turnover of 10 other SAM-dependent riboswitches was also initiated by RNase Y. Depletion of this ribonuclease increased the half-life of bulk mRNA more than two-fold. This indicates that RNase Y might be not only important for riboswitch RNA turnover but also as a key player in the initiation of mRNA decay in B. subtilis. About 40% of the sequenced eubacterial species have an RNase Y orthologue.