STATIONARY PHASE-SPECIFIC EXPRESSION OF THE FIC GENE IN ESCHERICHIA-COLI K-12 IS CONTROLLED BY THE RPOS GENE-PRODUCT (SIGMA(38))

The pc gene, near pabA located at 75 min of the Escherichia coli chromosome, was previously identified as the regulatory factor of cell division. In this paper we have examined how pc gene expression is controlled during the growth cycle using a fic-lacZ protein fusion plasmid (pFL1). Its expression was induced at stationary phase while it was nearly abolished in rpoSmutants. Using a RNase protection assay, fic transcript at stationary phase was detected in rpoS(+) strains, but not in the rpoS mutants. Furthermore, primer extension analysis indicated that the pc transcript controlled by RpoS initiates at a G located 185 bp upstream from ATG of the fic coding region. Compared with the sigma(70) recognition sequence, the -10 region of pc promoter resembled the Pribnow box, but no homologous sequence was observed at the -35 region. These results were consistent with the characteristic sequence profile of fic promoter recognized specifically by RpoS in vitro, which is the only example of the type III promoter so far detected in vitro and in vivo.