FLAGELLIN, A MAJOR PROTEIN PRESENT IN SDS-PAGE PROFILES OF SARKOSYL-OMP-ENRICHED FRACTIONS FROM BORDETELLA-BRONCHISEPTICA BVG- OR MODULATEDBVG+ STRAINS

The bvg or vir locus positively regulates the expression of many Borde tella virulence-associated determinants (encoded by vag genes), includ ing cell envelope proteins, in response to environmental stimuli. On t he other hand several genes named vrg genes are negatively controlled by the bug regulon (Knapp and Mekalanos, 1988). Flagellin is encoded b y a vrg gene, which is expressed when the principal virulence factors are eliminated during antigenic modulation or in phase variants (Akerl ey et al., 1992). We have previously analyzed SDS-PAGE profiles of Sar kosyl-outer membrane protein (OMP)-enriched fractions from B. bronchis eptica Bvg- and modulated Bvg+ strains and reported a major band assoc iated with the avirulent phenotype (Passerini de Rossi et al., 1995). In order to characterize this band we have purified flagellar filament s from Bvg- and modulated Bvg+ strains, and analyzed them by SDS-PAGE. These profiles revealed a single major band of 40 or 45 kDa depending on the strain. The N-terminal amino acid sequence of the putative fla gellin expressed by BB7200a was identical over the first 21 residues a nalyzed to that of the flagellin from the modulated strain BB7865 repo rted by Akerley et al. (1992). Comparison of the SDS-PAGE profile of f lagellar filaments with that of the OMP-enriched fraction of the corre sponding strain showed that the flagellum-associated polypeptide had t he same electrophoretic mobility as that of the characteristic band of the avirulent phenotype. Furthermore, this band was absent in the OMP -enriched fraction profile from a Bvg strain subjected to a treatment that removes flagella. Our results indicate that the major protein obs erved in SDS-PAGE profiles of Sarkosyl-OMP-ttnriched fractions from B. bronchiseptica Bvg- and modulated Bvg+ strains corresponds to flagell in.