In recent years, it has become increasingly evident that post-transcriptional control mechanisms are the principal source of gene regulation for a large number of prokaryotic genetic pathways, particularly those involved in virulence and environmental adaptation. Post-transcriptional regulation is largely governed by RNA stability, which itself is determined by target accessibility to RNase degradation. In most Firmicutes species, mRNA stability is strongly impacted by the activity of two recently discovered RNases referred to as RNase J1 and RNase J2. Little is known about RNase J1 function in bacteria and even less is known about RNase J2. In the current study, we mutated both RNase J orthologues in Streptococcus mutans to determine their functional roles in the cell. Single and double RNase J mutants were viable, but grew very slowly on agar plates. All of the mutants shared substantial defects in growth, morphology, acid tolerance, natural competence and biofilm formation. However, most of these defects were more severe in the RNase J2 mutant. Phenotypic suppression results also implicate a role for RNase J2 as a regulator of RNase J1 function. Unlike Bacillus subtilis, RNase J2 is a major pleiotropic regulator in S. mutans, which indicates some fundamental differences from B. subtilis in global gene regulation. Key conserved residues among the RNase J2 orthologues of lactic acid bacteria may hint at a greater role for RNase J2 in these species.
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