Regulation of RpoS, the Stationary Phase Sigma Factor, by RbsD

RpoS is the master regulator of stationary phase in bacteria. In response to stress, the RpoS protein accumulates and activates the stationary phase response which makes the cells go dormant and provides protection. A screen for regulators of RpoS was carried out with an overexpression library and an RpoS’-’LacZ fusion. Overexpression of the rbsD gene, which codes for a ribose pyranase necessary for efficient metabolism of ribose, was found to reduce RpoS levels. Using a beta-galactosidase assay and Western blot analysis, we found that the effect of rbsD on RpoS is mostly at the post-transcriptional level and the rbsD knock-out does not affect RpoS. In addition, ribose also lowered RpoS levels. In summary, the identification of rbsD as a regulator or RpoS sheds light on how ribose affects RpoS levels.