TEMPORAL AND SPATIAL REGULATION OF FLIP, AN EARLY FLAGELLAR GENE OF CAULOBACTER-CRESCENTUS THAT IS REQUIRED FOR MOTILITY AND NORMAL-CELL DIVISION

In Caulobacter crescentus, the genes encoding a single polar flagellum are expressed under cell cycle control. In this report, we describe t he characterization of two early class II flagellar genes contained in the orfX-fliP locus. Strains containing mutations in this locus exhib it a filamentous growth phenotype and fail to express class III and IV flagellar genes. A complementing DNA fragment was sequenced and found to contain two potential open reading frames; The first, orfX, is pre dicted to encode a 105-amino-acid polypeptide that is similar to MopB, a protein which is required for both motility and virulence in Erwini a carotovora. The deduced amino acid sequence of the second open readi ng frame, fliP, is 264 amino acids in length and shows significant seq uence identity with the FliP protein of Escherichia coli as well as vi rulence proteins of several plant and mammalian pathogens. The Flip ho molog in pathogenic organisms has been implicated in the secretion of virulence factors, suggesting that the export of virulence proteins an d some flagellar proteins share a common mechanism. The 5' end of orfX -fliP mRNA was determined and revealed an upstream promoter sequence t hat shares few conserved features with that of other early Caulobacter flagellar genes, suggesting that transcription of orfX-fliP may requi re a different complement of trans-acting factors. In C. crescentus, o rfX-fliP is transcribed under cell cycle control, with a peak of trans criptional activity in the middle portion of the cell cycle. Later in the cell cycle, orfX-fliP expression occurs in both poles of the predi visional cell. Protein fusions to a lacZ reporter gene indicate that F liP is specifically targeted to the swarmer compartment of the predivi sional cell.