Control of bacteriophage lambda cII activity by bacteriophage and host functions

We have studied the regulation of the λ cII gene in vivo using cloned λ fragments. Lambda N protein stimulated cII expression. Surprisingly, although very high cII protein levels were detected by gel electrophoresis, little cII protein activity, measured as stimulation of the λ p(I) and p(E) promoters, was observed. The half-life of cII protein dependend critically on its initial level. At low concentrations its half-life was as short as 1.5 min, whereas at high cII protein levels, it could be as long as 22 min. The Escherichia coli mutant ER437 directs λ towards lysogeny; cII protein was more stable in this strain than in the wild type. On the other hand, although cyclic AMP is required for efficient lysogeny, it did not appear to influence the synthesis, stability, or activity of cII protein.