Three Ribosomal Operons of Contain Genes Encoding Small RNAs That Interact With Hfq and CsrA .

Three out of the seven ribosomal RNA operons in end in dual terminator structures. Between the two terminators of each operon is a short sequence that we report here to be an sRNA gene, transcribed as part of the ribosomal RNA primary transcript by read-through of the first terminator. The sRNA genes (, and ) from the three operons (, and ) are more than 98% identical, and pull-down experiments show that their transcripts interact with Hfq and CsrA. Deletion of , as well as overexpression of , only modestly affect known CsrA-regulated phenotypes like biofilm formation, translation and translation, and the role of the sRNAs may not yet be fully understood. Since RrA, B, F are short-lived and transcribed along with the ribosomal RNA components, their concentration reflect growth-rate regulation at the ribosomal RNA promoters and they could function to fine-tune other growth-phase-dependent processes in the cell. The primary and secondary structure of these small RNAs are conserved among species belonging to different genera of Enterobacteriales.