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A riboswitch-regulated antisense RNA in Listeria monocytogenes
- Mellin, J. R., Tiensuu, Teresa, Bécavin, Christophe, Gouin, Edith, Johansson, Jörgen, Cossart, Pascale
- Proceedings of the National Academy of Sciences of the United States of America 2013 v.110 no.32 pp. 13132-13137
- Listeria monocytogenes, Salmonella enterica, antisense RNA, bacteria, enzymes, genes, messenger RNA, metabolism, non-coding RNA, pathogenesis, transcription (genetics), transcription factors
- Riboswitches are ligand-binding elements located in 5′ untranslated regions of messenger RNAs, which regulate expression of downstream genes. In Listeria monocytogenes , a vitamin B ₁₂-binding (B ₁₂) riboswitch was identified, not upstream of a gene but downstream, and antisense to the adjacent gene, pocR, suggesting it might regulate pocR in a nonclassical manner. In Salmonella enterica, PocR is a transcription factor that is activated by 1,2-propanediol, and subsequently activates expression of the pdu genes. The pdu genes mediate propanediol catabolism and are implicated in pathogenesis. As enzymes involved in propanediol catabolism require B ₁₂ as a cofactor, we hypothesized that the Listeria B ₁₂ riboswitch might be involved in pocR regulation. Here we demonstrate that the B ₁₂ riboswitch is transcribed as part of a noncoding antisense RNA, herein named AspocR. In the presence of B ₁₂, the riboswitch induces transcriptional termination, causing aspocR to be transcribed as a short transcript. In contrast, in the absence of B ₁₂, aspocR is transcribed as a long antisense RNA, which inhibits pocR expression. Regulation by AspocR ensures that pocR , and consequently the pdu genes, are maximally expressed only when both propanediol and B ₁₂ are present. Strikingly, AspocR can inhibit pocR expression in trans , suggesting it acts through a direct interaction with pocR mRNA. Together, this study demonstrates how pocR and the pdu genes can be regulated by B ₁₂ in bacteria and extends the classical definition of riboswitches from elements governing solely the expression of mRNAs to a wider role in controlling transcription of noncoding RNAs.