Rabbit polyclonal antibody to PR (A394)

The effects of progesterone are mediated by two functionally different isoforms of the progesterone receptor, PR~A and PR~B, which are transcribed from distinct, estrogen inducible promoters within a single copy of the PR gene. The PR~A and PR~B proteins are 90 kDa and 118 kDa respectively; the first 164 amino acids of PR~B are absent in PR~A. Progesterone bound PR~A and PR~B have different transcription activation properties. Specifically, PR~B functions as a transcriptional activator in most cell and promoter contexts, while PR~A is transcriptionally inactive and functions as a strong ligand dependent transdominant repressor of steroid hormone receptor transcriptiona activity. An inhibitory domain (ID), which maps to the amino terminus of the receptor, exists within both PR isoforms.