riboswitch-regulated antisense RNA in Listeria monocytogenes

• Published in: Proceedings of the National Academy of Sciences - PNAS 2013-08, Vol.110 (32), p.13132-13137
• Main Authors: Mellin, J. R., Tiensuu, Teresa, Bécavin, Christophe, Gouin, Edith, Johansson, Jörgen, Cossart, Pascale
• Format: Article
• Language: English
• Subjects: Antisense RNA; Bacteria; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Base Sequence; Biological Sciences; Blotting, Northern; Blotting, Western; Gene expression; Gene expression regulation; Gene Expression Regulation, Bacterial; Genes; Genetic loci; Hydro-Lyases - genetics; Hydro-Lyases - metabolism; Listeria; Listeria monocytogenes; Listeria monocytogenes - genetics; Listeria monocytogenes - metabolism; Messenger RNA; Mutation; Pathogenesis; Propylene Glycol - metabolism; Propylene glycols; Protein Binding; Reverse Transcriptase Polymerase Chain Reaction; Ribonucleic acid; Riboswitch - genetics; RNA; RNA Stability - genetics; RNA, Antisense - genetics; RNA, Antisense - metabolism; RNA, Messenger - genetics; RNA, Messenger - metabolism; Sequence Homology, Nucleic Acid; Transcription Factors - genetics; Transcription Factors - metabolism; Vitamin B 12 - metabolism
• ISSN: 0027-8424; 1091-6490; 1091-6490
• DOI: 10.1073/pnas.1304795110

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.