Genetic Analysis of O-H Variation in Salmonella

H1 inactive mutants from diphasic strain of S. typimurium perform O-H variation in place of phase variation. Phase-1 is O type and phase-2 is H type in such mutants. The functions of H1 and H2 are duplicate in flagellar production. The activity of H1 is controlled by Ah1, which is closely linked to H1 but separable from it by recombination. The mutation of Ah1+ to Ah1- causes the inactivation of H1. The mutant sites of three Ah1- strains differ from each other in a single cistron, and they have different potentiality of reversion.