Identification of Escherichia coli region III flagellar gene products and description of two new flagellar genes.

Region III flagellar genes in Escherichia coli are involved with the assembly and rotation of the flagella, as well as taxis. We subcloned the flaB operon from a lambda fla transducing phage onto plasmid pMK2004. Two additional genes were found at the flaB locus, and we subdivided the flaB gene into flaB1, flaBII, and flaBIII. The cheY suppressor mutations which have previously been mapped to flaB were further localized to flaB11 (Parkinson et al., J. Bacteriol. 155:265-274, 1983). Until now, gene product identification has not been possible for these genes because of their low levels of gene expression. Overexpression of the flagellar genes was accomplished by placing the flaB operon under the control of the lacUV5 or tac promoters. Plasmid-encoded proteins were examined in a minicell expression system. By correlating various deletions and insertions in the flaB operon with the ability to complement specific flagellar mutants and code for polypeptides, we made the following gene product assignments: flaB 1, 60 kilodaltons; flaB 11, 38 kilodaltons; flaB111, 28 kilodaltons; flaC, 56 kilodaltons; fla0, 16 kilodaltons; and flaE, 54 kilodaltons.