IDENTIFICATION OF A NOVEL ESCHERICHIA-COLI GENE WHOSE EXPRESSION IS DEPENDENT ON THE FLAGELLUM-SPECIFIC SIGMA-FACTOR, FLIA, BUT DISPENSABLEFOR MOTILITY DEVELOPMENT

FliA is an alternative sigma factor specific for class 3 flagellar ope rons. Using a promoter-probe vector, we randomly cloned Escherichia co li DNA fragments, which showed FliA-dependent promoter activities. Amo ng the DNA fragments cloned, one was found to be derived from a non-fl agellar region. Hybridization analysis with the Kohara E. coli library indicated that this DNA fragment is located at around 35.4 min on the E. coli chromosome where no flagellar gene has been reported yet. DNA sequence analysis revealed that it contains an FliA-dependent promote r-like sequence followed by an open reading frame (ORF) that can encod e a 110-amino-acid protein. A rho-independent terminator-like sequence follows this ORF. This putative gene was named flxA. A gene disruptan t was constructed by inserting the kan gene cassette into the flxA gen e on the chromosome. This mutant was found to be actively motile, sugg esting that this gene is unlikely to be involved in the motility pheno type of E. coli. (C) 1997 Elsevier Science B.V.