Mutational analysis of the chicken progesterone receptor

Oligonucleotide-directed site mutagenesis was used to prepare a series of chicken progesterone receptor deletion mutants in an attempt to elucidate structure-function relationships of the receptor. These mutants spanned the entire 659-amino acid coding region of the A form of the receptor. The ability of these mutants to bind progesterone was analyzed following in vitro transcription and translation. Results obtained indicate that a large portion of the protein ranging from amino acid 420 to the extreme carboxyl terminus is necessary to maintain the protein in a conformation which is capable of binding hormone. Following transient cotransfection of mutant receptor proteins into CV-1 cells along with a receptor gene containing an authentic GRE/PRE (PRE-TK-CAT), our results indicated that any deletion throughout the entire molecule results in a decrease in transcriptional activation. Most of these decreases result from an inability of the mutant receptor proteins to bind DNA or hormone. However, two areas of the receptor have been identified which are unrelated to either DNA or hormone binding but markedly affect the ability of the receptor to transactivate target genes.