The flgE gene of Campylobacter coli is under the control of the alternative sigma factor σ⁵⁴

The flgE gene encoding the flagellar hook protein of Campylobacter coli VC167-T1 was cloned by immunoscreening of a genomic library constructed in λZAP Express. The flgE DNA sequence was 2,553 bp in length and encoded a protein with a deduced molecular mass of 90,639 Da. The sequence had significant homology to the 5' and 3' sequences of the flgE genes of Helicobacter pylori, Treponema phagedenis, and salmonella typhimurium. Primer extension analysis indicated that the VC167 flgE gene is controlled by a σ⁵⁴ promoter. PCR analysis showed that the flgE gene size and the 5' and 3' DNA sequences were conserved among C. coli and C. jejuni strains. Southern hybridization analyses confirmed that there is considerable sequence identity among the hook genes of C. coli and C. jejuni but that there are also regions within the genes which differ. Mutants of C. coli defective in hook production were generated by allele replacement. These mutants were nonmotile and lacked flagellar filaments. Analyses of flgE mutants indicated that the carboxy terminus of FIgE is necessary for assembly of the hook structure but not for secretion of FlgE and that, unlike salmonellae, the lack of flgE expression does not result in repression of flagellin expression.