Bacteriophage lambda cro mutations: effects on activity and intracellular degradation.

Following random mutagenesis of the bacteriophage lambda cro gene, we have isolated missense mutations that affect approximately half of the 66 residue positions of Cro. About two-thirds of the mutations change residues involved in the maintenance of Cro structure and stability. The corresponding mutant proteins are severely degraded in the cell but often have specific activities near that of wild-type Cro. The remaining mutations affect residues involved in DNA binding. These mutant proteins are present at moderately reduced intracellular levels, but their specific activities are much lower than that of wild type.