TI  - Characterization of a novel 23-kilodalton protein of unactive progesterone
      receptor complexes.
PG  - 1956-63
AB  - Immunoprecipitation of unactivated avian progesterone receptor results in
      the copurification of <prot>hsp90</prot>, <prot>hsp70</prot>, and three additional proteins, <prot>p54</prot>,
      <prot>p50</prot>, and <prot>p23</prot>. <prot>p23</prot> is also present in immunoaffinity-purified <prot>hsp90</prot>
      complexes along with <prot>hsp70</prot> and another protein, <prot>p60</prot>. Antibody and cDNA
      probes for <prot>p23</prot> were prepared in an effort to elucidate the significance
      and function of this protein. Antibodies to <prot>p23</prot> detect similar levels of
      <prot>p23</prot> in all tissues tested and cross-react with a protein of the same size
      in mice, rabbits, guinea pigs, humans, and Saccharomyces cerevisiae,
      indicating that <prot>p23</prot> is a conserved protein of broad tissue distribution.
      These antibodies were used to screen a chicken brain cDNA library,
      resulting in the isolation of a 468-bp partial cDNA clone encoding a
      sequence containing four sequences corresponding to peptide fragments
      isolated from chicken <prot>p23</prot>. This partial clone was subsequently used to
      isolate a full-length human cDNA clone. The human cDNA encodes a protein
      of 160 amino acids that does not show homology to previously identified
      proteins. The chicken and human cDNAs are 88% identical at the DNA level
      and 96.3% identical at the protein level. <prot>p23</prot> is a highly acidic
      phosphoprotein with an aspartic acid-rich carboxy-terminal domain.
      Bacterially overexpressed human <prot>p23</prot> was used to raise several monoclonal
      antibodies to <prot>p23</prot>. These antibodies specifically immunoprecipitate  <prot>p23</prot>  in
      complex with  <prot>hsp90</prot>  in all tissues tested and can be used to immunoaffinity
      isolate progesterone receptor complexes from chicken oviduct cytosol.
AD  - Department of Biochemistry and Molecular Biology, Mayo Graduate School,
