Homodimer formation is rate-limiting for high affinity DNA binding by glucocorticoid receptor.

The glucocorticoid receptor (GR) is a hormone-inducible transcription factor which activates transcription of specific genes by binding to a DNA sequence present in the promoters of inducible genes. These glucocorticoid response elements (GREs) have a conserved palindromic sequence. Each half-GRE palindrome binds one subunit of GR. We have assessed the relative affinity of GR monomers and homodimers for GRE and determined whether homodimer formation is rate-limiting for high affinity GRE binding. The in vitro affinity of GRE binding by GR homodimers was approximately 2 x 10(-10) M, whereas it was approximately 1 nM for GR monomers. While homodimer:GRE complexes were very stable, monomer:GRE complexes appeared less stable in vitro. At low receptor concentration, GR preferentially bound GRE as a homodimer. Prior dilution of GR (equilibrium shifted to monomers) before addition to a GRE binding reaction resulted in slower kinetics of binding by comparison to parallel reactions in which concentrated (largely h...