Agrobacterium tumefaciens possesses a fourth flagellin gene located in a large gene cluster concerned with flagellar structure, assembly and motility

The authors have identified a fourth flagellin gene in a 21850 bp region of the Agrobacterium tumefaciens C58C1 chromosome containing at least 20 gene s concerned with flagellar structure, assembly and function. Three flagelli n genes, flaA, flaB and flaC, orientated rightward, are positioned in a tan dem array at the right end, with the fourth, substantially larger gene, fla D, in the opposite orientation, at the left end. Between these lie four app arent operons, two transcribed in each direction (motA, flhB leftward; flgF , flgB rightward) from a divergent position approx 7.5 kb from the left end . This unifies the previously published motA, flgB and flaABC sequences int o a single region, also containing the homologues of flhB, flgF and fliI. S ite-specific mutagenesis of fliI results in a non-flagellate phenotype, whi le a Tn5-induced flhB mutant possesses abnormal flagella. Mutagenesis and p rotein profiling demonstrate that all four flagellins contribute to flagell ar structure: FlaA is the major protein, FlaB and FlaC are present in lesse r amounts, and FlaD is a minor component. FlaA has anomolous electrophoreti c mobility, possibly due to glycosylation.