THE YDJ1 MOLECULAR CHAPERONE FACILITATES FORMATION OF ACTIVE P60(V-SRC) IN YEAST

Molecular chaperones have been implicated in the formation of active p 60(v-src) tyrosine kinase. In Saccharomyces cerevisiae, expression of p60(v-src) causes cell death, a phenomenon that requires functional Hs p90. We show here that mutations in a member of a second class of chap erones, the yeast dnaJ homologue YDJ1, suppress the lethality caused b y p60(v-src). One p60(v-src)-resistant ydj1 mutant, ydj1-39, which has two point mutations in the highly conserved ''J'' domain, has reduced levels of v-src mRNA and protein. However, a ydj1 null mutant produce s normal quantities of active p60(v-src), indicating that Ydj1p facili tates, but is not essential for, the formation of active p60(v-src). W e also report p60(v-src)-resistance in a previously identified tempera ture-sensitive ydj1 mutant, ydj1-151. In this mutant, the level of p60 (v-src) remains unaltered, but the protein is much less active in vivo . In addition, p60(v-src) immunoprecipitates from the ydj1-151 strain contained Hsp90 and Hsp70 in greater amounts than in wild-type strains . Ydj1 protein was also detected in p60(v-src) immunoprecipitates from both wild-type and ydj1-151 strains. These results indicate that Ydj1 p participates in the formation of active p60(v-src) via molecular cha perone complexes.