Mutations in the right operator of bacteriophage lambda: Physiological effects

Abstract

The right operator in bacteriophage lambda vs326 has one-twentieth the in vitro binding affinity for repressor as λv +; for comparison λv3 has one-quarter the affinity of λv +. In vivo, both mutants constitutively express genes in the right operon. Both λv3 and λvs326 express gene O constitutively because they complement λimm434 Oam − in a λ lysogen, vs, more efficiently than v3. The v3 allele in cis (but not in trans) to vs326 gives significantly greater phage yields in a λ lysogen than λvs326 alone, cro gene function, measured by arrest of exonuclease synthesis, suggested the following series of increasing degree of conatitutivity: v3, vs326, v3 vs326. λv2 vs326 forms plaques on lysogens that carry λ cI857, but λv2 v3 does not. These results indicate that vs326, like v3, is an operator constitutive mutation but stronger in its effects. These mutants exemplify a uniform correlation between relative weakness of repressor binding and degree of constitutive gene expression.