Subunit dissociation affects DNA binding in a dimeric lac repressor produced by C-terminal deletion.

摘要: The reduction in apparent operator binding affinity found for dimeric lac repressor proteins produced by disruption of the C-terminal coiled-coil interaction has been proposed to derive from thermodynamic linkage between dimer-monomer and protein-DNA equilibria [Brenowitz et al. (1991) J. Biol. Chem. 266, 1281]. To explore this linkage, we have employed two proteins, a deletion mutant (-11 aa) missing 11 amino acids at C-terminus that diminished [Chen & Matthews (1992) 267, 13843] (R3) binds with wild-type which leucine heptad repeats were replaced GCN4 dimerization sequence [Alberti (1993) EMBO 12, 3227; Chen (1994) (in press)]. avoid complexities working low concentrations protein required high monomer subunits, urea denaturation studies undertaken determine free energy change(s) dissociation and/or unfolding. Under denaturing conditions, dimer unfolding be concerted processes, change overall process unfolded was derived these experiments proteins. A monomeric (Y282D) lactose examined protomer From combination data, Kd -11 aa determined 7.7 x 10(-8) M, corresponding value R3 3.2 10(-11) M.(ABSTRACT TRUNCATED AT 250 WORDS)