Main content area

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.