EXPRESSION OF ESCHERICHIA-COLI PYRUVATE OXIDASE (POXB) DEPENDS ON THESIGMA-FACTOR ENCODED BY THE RPOS(KATF) GENE

The activity of Escherichia coli pyruvate oxidase (PoxB) was shown to be growth-phase dependent; the enzyme activity reaches a maximum at ea rly stationary phase. We report that PoxB activity is dependent on a f unctional rpoS(katf) gene which encodes a a factor required to transcr ibe a number of stationary-phase-induced genes. PoxB activity as well as the beta-galactosidase encoded by a poxB::lacZ protein fusion was c ompletely abolished in a strain containing a defective rpoS gene. Nort hern and primer extension analyses showed that poxB expression was reg ulated at the transcriptional level and was transcribed from a single promoter; the 5' end of the mRNA being located 27 bp upstream of the t ranslational initiation codon of poxB. The poxB gene was expressed at decreased levels under anaerobiosis; however, the anaerobic regulatory genes arcA, arcB or fnr were not involved in anaerobic poxB gene expr ession. Expression of the rpoS(katF) gene has been reported to be affe cted by acetate, the product of PoxB reaction. However, we found that poxB null mutations had no effect on rpoS(katF) expression. inactivati on of two genes involved in acetate metabolism, ackA and pta, had no e ffect on either poxB or rpoS(katF) expression.