CHARACTERIZATION OF CYCLOPHILIN-40 - HIGHLY CONSERVED PROTEIN THAT DIRECTLY ASSOCIATES WITH HSP90

Cyclophilin 40 (CyP40) is a recently identified member of the cyclophi lin family that may be a component of unactivated steroid receptor com plexes, It consists of an N-half portion that is highly homologous to cyclophilin A and has peptidyl prolyl isomerase (PPIase) activity, and a C-half portion that resembles the C-terminal portion of FKBP52 (FK5 06 binding protein 52), another component of unactivated steroid recep tor complexes, To better understand the structure and functional chara cteristics of this new class of cyclophilin, we have raised monoclonal antibodies against the C-half portion of human CyP40, Immunostaining with the antibodies showed its preferential localization in cytoplasm, One antibody cross-reacted with a 45 kDa protein in yeast, suggesting high conservation throughout evolution, A CyP40-associated protein wa s isolated from rabbit reticulocyte lysate by means of an affinity res in, and was identified as hsp90. The C-half portion of CyP40 was neces sary and sufficient for the interaction.