IDENTIFICATION OF SIGMA(S)-REGULATED GENES IN SALMONELLA-TYPHIMURIUM - COMPLEMENTARY REGULATORY INTERACTIONS BETWEEN SIGMA(S) AND CYCLIC-AMP RECEPTOR PROTEIN

sigma(s) (RpoS)-regulated lacZ transcriptional fusions in Salmonella t yphimurium were identified from a MudJ transposon library by placing t he rpoS gene under the control of the araBAD promoter and detecting la cZ expression in the presence or absence of arabinose supplementation. Western blot (immunoblot) analysis of bacteria carrying P-BAD::rpoS d emonstrated arabinose-dependent rpoS expression during all phases of g rowth. sigma(s)-dependent gene expression of individual gene fusions w as confirmed by P22-mediated transduction of the MudJ insertions into wild-type or rpoS backgrounds. Analysis of six insertions revealed the known sigma(s)-regulated gene otsA, as well as five novel loci. Each of these genes is maximally expressed in stationary phase, and all but one show evidence of cyclic AMP receptor protein-dependent repression during logarithmic growth which is relieved in stationary phase. For these genes, as well as for the sigma(s)-regulated spvB plasmid virule nce gene, a combination of rpoS overexpression and crp inactivation ca n result in high-level expression during logarithmic growth. The appro ach used to identify sigma(s)-regulated genes in this study provides a general method for the identification of genes controlled by trans-ac ting regulatory factors.