An analysis of ecdysone receptor domains required for heterodimerization with ultraspiracle

We have prepared several truncated versions of the Choristoneura fumiferana ecdysone receptor (CfEcR) cDNA to identify domains required for heterodime rization with C. fumiferana ultraspiracle (CfUSP), The CfEcR protein contai ning all six domains bound to hsp27 EcRE in the presence of CfUSP protein. The only regions that could be deleted from CfEcR without losing DNA bindin g activity were A/B and F domains as well as a 29 amino acid region located at the C-terminal end of the E domain. This suggests that the minimum regi on required for DNA binding is a 363 amino acid peptide spanning C, D, and part of E domains. The CfEcR protein containing all six domains bound ponas terone A, in the presence of CfUSP protein, Removal of the F domain and the C-terminal 12 amino acids in the E domain completely abolished ponasterone A binding. Removal of A/B and C domains did not affect ligand binding, How ever, deleting the D domain abolished ligand binding completely. The minimu m region required for ligand binding is a 333 amino acid peptide spanning t he D, E, and F domains. The A/B region is the only domain that can be delet ed without affecting both DNA and ligand binding of CfEcR. These results su ggest that CfEcR has two sub domains in the D and E domains that are necess ary for heterodimerization with the CfUSP protein, Arch. Insect Biochem, Ph ysiol, 41:61-70, 1999. (C) 1999 Wiley-Liss, Inc.