P22 c2 repressor. Domain structure and function.

The c2 repressor of bacteriophage P22 can be digested with trypsin, chymotrypsin, or elastase to yield stable fragments. Purified NH2-terminal fragments, like intact repressor, bind specifically to P22 operator DNA and also mediate positive and negative control of transcription. COOH-terminal fragments of repressor do not bind operator DNA but do undergo a concentration-dependent oligomerization similar to that observed with intact repressor. These results suggest that P22 repressor, like the related cI repressor of phage lambda, contains two structural domains which mediate different functions of the intact molecule.