hsp108,,,,,, a novel heat shock inducible protein of chicken

cDNA clones encoding a protein that copurifies with the progesterone receptor B subunit but does not bind progesterone have been described [Kulomaa, M. S., Weigel, N. L., Kleinsek, D. A., Beattie, W. G., Conneely, O. M., March, C., Zarucki-Schulz, T., Schrader, W. T., & O'Malley, B. W. (1986) Biochemistry (preceding paper in this issue)]. A full-length sequence for these clones was derived and was found to encode a protein that is structurally unrelated to the progesterone receptor but that contains significant homologies to the previously described heat shock proteins hsp90 of yeast and hsp83a of Drosophila melanogaster. In this paper it is shown that this protein is indeed a heat shock protein. Though the apparent molecular weight of the protein is 108,000 on sodium dodecyl sulfate-polyacrylamide gels, the molecular weight of the polypeptide backbone is 92,000. The steady-state level of gene transcripts as well as the level of protein is inducible by heat shock, but the gene is constitutively expressed in a number of tissues. A previously undescribed heat shock protein of molecular weight 78,000 in these preparations is also reported.