Photochemical attachment of lac repressor to bromodeoxyuridine-substituted lac operator by ultraviolet radiation

The transducing phage lambdah80dlac carries the lac operator, whereas wild-type lambdah80 does not. We find that in high salt (0.18 M KCl), ultraviolet radiation causes the formation of a very stable complex between repressor and 5-bromodeoxyuridine (BrdU)-substituted lambdah80dlac but not to BrdU-lambdah80 DNA. Studies with inducers of the lac operon confirm the specificity of attachment. In low slat (0.01 M KCl), ultraviolet radiation will also attach repressor nonspecifically to BrdU-lambdah80 DNA. The stability of the complex suggests that covalent bonds are formed. We also report that another regulatory protein, the catabolite gene activator protein, can be attached similarly to DNA.