Identification of the rat adrenal zona fasciculata/reticularis specific protein, inner zone antigen (IZAg), as the putative membrane progesterone receptor

Using immunological methods, a protein specific to the inner zones of the r at adrenal cortex, and called inner zone antigen (IZAg), was previously sho wn to have two interrelated forms of 26 kDa (IZAg1) and 55-60 kDa (IZAg2), and to have an action on steroid hydroxylation. After two-dimensional gel e lectrophoresis, and immunoaffinity column purification, N-terminal amino-ac id analysis showed that the first 12 amino acids were identical to those of a recently described putative membrane located progesterone receptor (PPMR ). RT-PCR Tvas then used to generate the cDNA of this protein, using RNA ex tracted from rat adrenals. A glutathione S-transferase (GST)-fusion constru ct was expressed in Escherichia coli, and shown to generate an immunoreacti ve product of molecular mass consistent with its identification as IZAg1. M ore detailed examination of the distribution of this protein, not only in t he zona fasciculata/reticularis of the adrenal cortex, but also in the Leyd ig cell, kidney and liver, suggest it may have a role in steroid hormone sy nthesis and/or metabolism.