A new class of clear mutants from coliphage 434 hy not complementing CII and C3 mutants for lysogenization.

Abstract

Clear mutants which differ from regular C I , C II , CIIIand y mutants have been isolated from phage 434 hy. These mutants resemble C I mutants in plaque and spot phenotype but efficiently complement C I mutants for lysogenization. Like C II mutants, they do not complement authentic C II mutants for lysogenization but in contrast to C II mutants they also fail to complement C III mutants. They map between the lambda-434 non-homology region and Co 1 (aC II mutant). On account of this map position adjacent to C II the mutants of the new type are called C IIa . They arise from phage 434 hy with a frequency comparable to that of C I and C II mutants. Such mutants are also obtained from phage lambda but apparently not from phage b5. C IIa mutants would not fit into a picture of three independently acting cistrons C I , CII, and C III . The hypothesis is presented that C IIa and C II mutants are in the same structural gene. Two possibilities are discussed that would account for the complementation patterns: 1. C IIa mutants may block the expression of gene C III in cis position; or 2. the products of genes C II and C III function through an oligomeric complex they form.