The chicken progesterone receptor A and B isoforms are products of an alternate translation initiation event

Abstract

The chicken progesterone receptor A and B proteins differ by an additional 128 amino acids located at the N terminus of the B protein. Using site-directed mutagenesis, we demonstrate that these two proteins arise by alternate initiation of translation from two in-phase AUG codons located on a single mRNA transcript. Both proteins are transcriptionally active in terms of their ability to activate a progesterone-responsive target gene. These results suggest a functional significance for evolutionary conservation of two forms of this steroid receptor.