Dual-function sRNA encoded peptide SR1P modulates moonlighting activity of <i>B. subtilis</i> GapA

<p>SR1 is a dual-function sRNA from <i>B. subtilis</i> that acts as a base-pairing regulatory RNA and as a peptide-encoding mRNA. Both functions of SR1 are highly conserved. Previously, we uncovered that the SR1 encoded peptide SR1P binds the glycolytic enzyme GapA resulting in stabilization of <i>gapA</i> mRNA. Here, we demonstrate that GapA interacts with RNases Y and J1, and this interaction was RNA-independent. About 1% of GapA molecules purified from <i>B. subtilis</i> carry RNase J1 and about 2% RNase Y. In contrast to the GapA/RNase Y interaction, the GapA/RNaseJ1 interaction was stronger in the presence of SR1P. GapA/SR1P-J1/Y displayed <i>in vitro</i> RNase activity on known RNase J1 substrates. Moreover, the RNase J1 substrate SR5 has altered half-lives in a Δ<i>gapA</i> strain and a Δ<i>sr1</i> strain, suggesting <i>in vivo</i> functions of the GapA/SR1P/J1 interaction. Our results demonstrate that the metabolic enzyme GapA moonlights in recruiting RNases while GapA bound SR1P promotes binding of RNase J1 and enhances its activity.</p

A multistress responsive type I toxin-antitoxin system: <i>bsrE</i>/SR5 from the <i>B. subtilis</i> chromosome

<p><i>bsrE</i>/SR5 is a type I TA system from prophage-like element P6 of the <i>B. subtilis</i> chromosome. The 256 nt <i>bsrE</i> RNA encodes a 30 aa toxin. The antitoxin SR5 is a 163 nt antisense RNA. Both genes overlap at their 3′ ends. Overexpression of <i>bsrE</i> causes cell lysis on agar plates, which can be neutralized by <i>sr5</i> overexpression, whereas deletion of the chromosomal <i>sr5</i> copy has no effect. SR5 is short-lived with a half-life of ≈7 min, whereas <i>bsrE</i> RNA is stable with a half-life of >80 min. The <i>sr5</i> promoter is 10-fold stronger than the <i>bsrE</i> promoter. SR5 interacts with the 3′ UTR of <i>bsrE</i> RNA, thereby promoting its degradation by recruiting RNase III. RNase J1 is the main RNase responsible for SR5 and <i>bsrE</i> RNA degradation, and PnpA processes an SR5 precursor to the mature RNA. Hfq stabilizes SR5, but is not required for its inhibitory function. While <i>bsrE</i> RNA is affected by temperature shock and alkaline stress, the amount of SR5 is significantly influenced by various stresses, among them pH, anoxia and iron limitation. Only the latter one is dependent on <i>sigB</i>. Both RNAs are extremely unstable upon ethanol stress due to rapid degradation by RNase Y.</p