Studies on partially virulent mutants of lambda bacteriophage

Summary Genetic studies coupled with functional analysis of gene action have demonstrated that there are two classes of partially virulent CP mutants which differ in the mechanism by which they overcome the immunity repressor. Class I contains a mutation within the cI region which causes the modified cI product to negatively complement the active repressor present in the immune cells. Class II achieve their virulence by a mutation which renders the x-y-cII-O operon insensitive to repression.