IDENTIFICATION OF GENES NEGATIVELY REGULATED BY FIS - FIS AND RPOS COMODULATE GROWTH-PHASE-DEPENDENT GENE-EXPRESSION IN ESCHERICHIA-COLI

Fis is a nucleoid-associated protein in Escherichia coli that has been shown to regulate recombination, replication, and transcription react ions. It is expressed in a transient manner under batch culturing cond itions such that high levels are present during early exponential phas e and low levels are present during late exponential phase and station ary phase. We have screened a random collection of transposon induced lac fusions for those which give decreased expression in the presence of Fis, Thirteen different Fis-repressed genes were identified, includ ing glnQ (glutamine high-affinity transport), mglA (methyl galactoside transport), xylF (D-xylose-binding protein), sdhA (succinate dehydrog enase flavoprotein subunit), and a newly identified aldehyde dehydroge nase, aldB. The LacZ expression patterns revealed that many of the fus ions mere maximally expressed at different stages of growth, including early log phase, mid- to late log phase, and stationary phase. The ex pression of some of the late-exponential- and stationary-phase genes w as dependent on the RpoS sigma factor, whereas that of others was affe cted negatively by RpoS. We conclude that Fis negatively regulates a d iverse set of genes and that RpoS can function to both activate and in hibit the expression of specific genes.