HSP90-CONTAINING MULTIPROTEIN COMPLEXES IN THE EUKARYOTIC MICROBE ACHLYA

In the oomycete fungus Achlya ambisexualis, hyphae of the male strain undergo sexual differentiation in the presence of the steroid hormone antheridiol. Earlier studies demonstrated that antheridiol binds with high affinity to a 9S multiprotein complex from A. ambisexualis cytoso ls. Although these complexes were found to contain the heat shock prot ein Hsp90, the other components were not known. It was of interest to determine if any of the other protein components in the Achlya Hsp90-h eterocomplexes would be homologous to those found in the steroid recep tor-Hsp90-heterocomplexes of vertebrates. Cytosolic proteins of 110 kD a, 74 kDa, 64 kDa, 61 kDa, 56 kDa, 47 kDa, 27 kDa and 23 kDa, were fou nd in repeated trials, to co-immunoprecipitate with Achlya Hsp90. The 74 kDa protein was identified as the heal shock protein Hsp70, the 23 kDa protein was found to be related to the vertebrate protein p23 and the 56 kDa protein was found to be related to immunophilin FKBP51. All three of these proteins are components of the vertebrate receptor het erocomplexes. The 110 kDa, 61 kDa and 27 kDa proteins appeared to be u nique to the Achlya complexes. Unlike the seven other proteins co-immu noprecipitating with Hsp90, the 61 kDa protein was observed only in th e co-immunoprecipitates produced from in vitro translates of RNA isola ted from antheridiol-treated mycelia.