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Dimerization of lambda cI repressor monomers is required for high-affinity binding to bacteriophage lambda operator DNA and is known to involve protein-protein contacts between C-terminal domains of the repressor monomers. In order to address the importance of the C-terminal domain in mediating the oligomeric properties of dimerization and cooperative binding to operator DNA, eight single-site mutant repressors were screened for possible deficiencies in cooperative interactions; all but one of the amino acid substitutions are located within the C-terminal domain. As a prelude to binding studies and the complete characterization of cooperativity mutants of lambda cI repressor (Burz, D. S., mutations at that site weaken, by 2-4 kcal/mol, the protein-protein interactions responsible for self-association. An additional mutant repressor, Pro158-->Thr, was also examined and found to associate reversibly from monomers to a species with stoichiometry greater than 2. All mutations increase the apparent Stokes radius of the monomeric form by 2-4.5 A and that of dimers by 1 or 3 A.
Burz et al. (Fri,) studied this question.