A NEW CLASS OF CLEAR MUTANTS FROM COLIPHAGE-434-HY NOT COMPLEMENTING C2 AND C3 MUTANTS FOR LYSOGENIZATION

Clear mutants which differ from regular CI, CII, C IIIand y mutants have been isolated from phage 434 hy. These mutants resemble CImutants in plaque and spot phenotype but efficiently complement CImutants for lysogenization. Like CIImutants, they do not complement authentic CIImutants for lysogenization but in contrast to CIImutants they also fail to complement CIIImutants. They map between the lambda-434 non-homology region and Co1 (aCIImutant). On account of this map position adjacent to CIIthe mutants of the new type are called CIIa. They arise from phage 434 hy with a frequency comparable to that of CIand CIImutants. Such mutants are also obtained from phage lambda but apparently not from phage b5. CIIamutants would not fit into a picture of three independently acting cistrons CI, CII, and CIII. The hypothesis is presented that CIIaand CIImutants are in the same structural gene. Two possibilities are discussed that would account for the complementation patterns: 1. CIIamutants may block the expression of gene CIIIin cis position; or 2. the products of genes CIIand CIIIfunction through an oligomeric complex they form. © 1969 Springer-Verlag.