Flagellar-phase variation: isolation of the rh1 gene

Abstract

In Salmonella, expression of flagellar antigen alternates between 2 serotypes (phases) encoded by 2 genes, H1 and H2. The mechanism which controls the alternative expression of the H1 and H2 genes was examined by cloning these genes and the genetic elements which control their activity on hybrid vehicles in E. coli. H2 gene activity was controlled by a recombinational switch located adjacent to the H2 gene. Activity of the H1 gene is thought to be repressed, when the H2 gene is expressed, by the product of another gene, rh1 (repressor of H1), which is controlled coordinately with the H2 gene. The construction of hybrid .lambda. vehicles which contain, besides the H2 gene, a genetic activity corresponding to rh1 is described. Variation of flagellar antigens analogous to that observed in Salmonella was observed when E. coli strains were transduced with the hybrid .lambda.. By using the .lambda.H2rh1 hybrid to program protein synthesis in UV-irradiated cells, the synthesis of a polypeptide was correlated with rh1 gene product activity. The H2 region apparently consists of 2 cotranscribed genes, H2 and rh1. The expression of both gene products is regulated by the same recombinational event.