Small non-coding RNAs and the bacterial outer membrane

Recent systematic genome searches revealed that bacteria encode a tremendous number of small non-coding RNAs (sRNAs). Whereas most of these molecules remain of unknown function, it has become increasingly clear that many of them will act to modulate gene expression at the post-transcriptional level. Where studied in more detail, sRNAs have often been found to control the expression of outer membrane proteins (OMPs). Enterobacteria such as Escherichia coli and Salmonella are now known to encode at least eight OMP-regulating sRNAs (InvR, MicA, MicC, MicF, OmrAB, RseX and RybB). These sRNAs exert their functions under a variety of growth and stress conditions, including the σE-mediated envelope stress response. An sRNA–OMP network is emerging in which some sRNAs act specifically on a single omp mRNA, whereas others control multiple omp mRNA targets.