Gene N regulator function of phage λ imm21: Evidence that a site of N action differs from a site of N recognition

Abstract

We report the isolation and characterization of a new mutation in the hybrid phage λ imm21. Both genetic and physiological studies demonstrate that this new mutation, N 21−1, is similar to N mutations of phage λ. As in the case of the N gene of λ (Ni λ), the N 21−1 mutation maps immediately to the left of the cI gene and has a pleiotropic effect on the expression of phage functions. Although these studies strongly suggest that phage 21 has an N function, they do not definitely locate the N 21−1 mutation within the N 21 structural gene. Reported here are studies demonstrating that N 21 acts in trans, similar to N λ, to stimulate the expression of phage functions. N products show an immunity specificity; N 21 being only active on phage carrying the immunity region of phage 21, while the n λ is only active on phage carrying the immunity region of λ or phage 434. However, one site of action for N λ can be rescued from phage 21. We propose that the specificity of an N function is determined by its sites of recognition and that these sites may be different from the sites of N action.