Coordinated regulation of the cI and int genes in coliphage λ and specificity of the cII/cIII activators

Expression of the cI (repressor) and int (integrase) genes in the λ lysogenic pathway has been studied by following protein synthesis in uv-irradiated cells. Gene expression following infection by λ⁺, a phage carrying an intact repressor gene, and by λvir, a phage carrying operator mutations with reduced affinity for the repressor, substantiated previous findings on the coordinated regulation of these two genes, and showed that their expression can be dissociated from that of other early genes. Experiments with λ hybrid phages showed that the cII gene products of λimm21 and of λimm22, which are of origin of phages 21 and P22, can activate Int synthesis from P_I of λ origin. Possible homology between the various cII genes is discussed.