ROLE OF THE CRO REPRESSOR CARBOXY-TERMINAL DOMAIN AND FLEXIBLE DIMER LINKAGE IN OPERATOR AND NONSPECIFIC DNA-BINDING

A series of mutations comprising single and multiple substitutions, deletions, and extensions within the carboxy-terminal domain of the bacteriophage λ Cro repressor have been constructed. These mutations generally affect the affinity of repressor for specific and nonspecific DNA. Additionally, substitution of the carboxy-terminal alanine with several amino acids capable of hydrogen-bonding interactions leads to improved specific binding affinities. A mutation is also described whereby cysteine links the two Cro monomers by a disulfide bond. As a consequence, a significant improvement in nonspecific binding and a concomitant reduction in specific binding are observed with this mutant. These results provide evidence that the carboxy terminus of Cro repressor is an important DNA binding domain and that a flexible connection between the two repressor monomers is a critical factor in modulating the affinity of wild-type repressor for DNA. © 1990, American Chemical Society. All rights reserved.