On flagellar formation in Caulobacter crescentus: novel flagellin synthesis in stub-forming non-motile mutants of C. crescentus.

Defective flagellar organella, stubs, and flagellin synthesis by L-[35S]methionine labeling of two non-motile mutants of C. crescentus CB15 were studied. CB15 wild type synthesized two flagellin species, flagellin A of molecular weight 26,000 and flagellin B of molecular weight 28,000. A DNA phage phi0CbK-resistant non-motile mutant, CB15 pdr-816 [Fukuda et al. (1981) J. Bacteriol. 145, 559-572] did not synthesize flagellin B but synthesized large amounts of flagellin A and a novel flagellin of smaller molecular weight 22,000 (22K flagellin), and formed stubs composed of both flagellin A and 22K flagellin. The other mutant, CB15 fla-801 synthesized only 22K flagellin and formed very short stubs composed of 22K flagellin. Motile revertants were isolated from these mutants. Full revertants were isolated from CB15 fla-801 at a frequency of ca. 10(-7). However, only partial revertants swimming slowly were obtained from CB15 pdr-816 at a similar frequency. Such partial revertants synthesized only flagellin A and formed short flagella in spite of the fact that flagellin A was still synthesized at a higher level than in the wild type. Given the previous finding that flagellin B first polymerizes onto the hook followed by addition of flagellin A onto flagellin B filament [Koyasu et al. (1981) J. Mol. Biol. 153, 471-475], flagellin B seems very important in the formation of normal flagella in C. crescentus. A small amount of 22K flagellin was detected even in wild type cell. Neither conversion nor alteration was observed in flagellin A or B or 22K flagellin by short-pulse and pulse-chase experiments. It was thus suggested that 22K flagellin was not a degradation product formed from other flagellins but was of different origin from flagellins A and B. C. crescentus flagellins consist of several subspecies of different isoelectric points. 22K flagellin consisted of at least three subspecies, in two-dimensional gel, with more basic isoelectric points than other flagellins. Heterogeneity in isoelectric point of polymerized and nascent flagellins was similar, indicating that each subspecies of different isoelectric point can polymerize into filament, and that conversion between subspecies is not needed to form flagellar filament.