THE LYSR-LIKE REGULATOR LEUO IN ESCHERICHIA-COLI IS INVOLVED IN THE TRANSLATIONAL REGULATION OF RPOS BY AFFECTING THE EXPRESSION OF THE SMALL REGULATORY DSRA-RNA

The translation of rpoS, which encodes the general stress sigma factor , sigma(S), in Escherichia coil, is stimulated by various stress condi tions, Regulatory factors involved in this control are the RNA-binding Hfq (HF-I) protein, the histone-like protein H-NS and the small regul atory DsrA-RNA (with the last being specifically required for increase d rpoS translation at low temperature), Here, we report the characteri zation of a transposon insertion mutant (Tn 10-8) with reduced sigma(S ) levels that led to the identification of an additional factor involv ed in the regulation of rpoS translation, the LysR-like regulator LeuO . Tn 10-8 decreases rpoS translation predominantly at low growth tempe rature, The mutation results in similarly strongly reduced DsrA-RNA ex pression and does not affect rpoS expression in a dsrA null mutant bac kground, indicating that it affects rpoS translation via DsrA-RNA, Tn 10-8 is inserted 26 bp upstream of the leuO open reading frame, which encodes a putative LysR-like regulator of unknown function, Instead of being a leuO null mutation, Tn 10-8 activates leuO expression as a re sult of the p(out) promoter on IS10(L) reading into leuO, indicating t hat LeuO represses dsrA and thereby reduces rpoS translation at low te mperature. LeuO does not contribute to temperature regulation of dsrA since its own expression is rather low and not temperature dependent, In a mutant deficient for H-NS, however, leuO is strongly derepressed, We conclude that rpoS translation is controlled by a regulatory netwo rk that includes Hfq, H-NS, LeuO and DsrA-RNA, In this network, H-NS p lays a dual role by interfering with rpoS translation in general and, via LeuO, influencing the synthesis of its own low-temperature antagon ist, DsrA-RNA.