Isolation and genetic analysis of operator-constitutive mutants of the H1 operon in Salmonella typhimurium.

In phase-2 cells of diphasic Salmonella strains, expression of H1 is repressor, coded for by the rh1 gene. A procedure for the isolation of operator-constitutive (H1-Oc) mutants of the H1 operon is described. Using three-factor crosses between an H1-Oc H1 strain and H1-O+ H1 strains, where motility recovery via H1-phase (or phase 1) flagellation was used as the selected marker and the H1-O character was the unselected marker, the relative position of the H1-Oc site to the H1 gene was determined. A diphasic H1-Oc strain produced, in phase 2, copolymer filaments composed of H1 and H2 flagellin.