Effect of the sRNA repeat RSs0680a-d on global gene regulation in Rhodobacter sphaeroides

In bacteria small RNAs (sRNAs) play an important role in response to stress situations by means of posttranscriptional gene regulation. Although there are few sRNAs that bind proteins, common sRNAs bind to target messenger RNAs (mRNAs) and modulate the stability and/or translation of the mRNA [1]. In Rhodobacter sphaeroides the expression of several such sRNAs is related to oxidative stress [2]. One sRNA that shows increased expression levels under oxidative stress is RSs0680a, which is cotranscribed with 3 homologous sRNAs (RSs0680b-d) and one hypothetical protein (RSP_6037). To realize stress dependent induction, the RSP_6037/RSs0680a-d operon is controlled by an RpoH_I/RpoH_II-dependent promoter [3]. We could show that constitutive overexpression of RSs0680a-d in R. sphaeroides leads to enhanced resistance to oxidative stress. Transcriptome and proteome analyses revealed serveral mRNAs and proteins with a changed abundance in the R. sphaeroides RSs0680a-d overexpression strain. Combination of those experiments with bioinformatic approaches revealed putative target mRNAs. Among these especially a putative operon of four genes shows lower levels of both the expressed mRNAs as well as the respective proteins. The genes in this operon are subunits of a putative aerobic carbon monoxide dehydrogenase and one hypothetical protein. A possible function of these genes is related to the oxidation of cytochrome b561, which is part of the membrane bound electron transport chain. Interestingly possible binding sites for RSs0680a can be detected 2-6 bp upstream of the AUGs of the four genes. Presently in vitro sRNA:mRNA interaction studies are performed, in order to prove the putative binding of RSs0680a to the mRNA of the putative operon.