Structure and function of the repressor of bacteriophage lambda

Abstract

By mutagenizing a λcIts (λcI857) lysogen, a λ mutant has been isolated with a wild-type phenotype. This mutant phage lysogenizes with low efficiency and produces a low burst. Though the initial rates of repressor synthesis in Escherichia coli after infection with wild-type and mutant λ are the same, the maximum level of repressor that is synthesized in the latter case is only about 30% of that synthesized in the former. Virulent λ plates on the lysogen of mutant λwith slightly less efficiency producing very tiny plaques. Operator-binding studies made in vitro with purified mutant and wild-type repressors show that the binding curve of the former repressor is a rectangular hyperbola while that of the latter is sigmoid. The half-lives of the complexes of mutant and wild-type repressors with right operator are 133 and 27 min, respectively. All these results suggest that the mutant repressor possibly has a higher affinity for the operators. This mutant has been named λcIha (ha=high affinity).