Type I HSP40 co-chaperone; regulates HSP90 and HSP70 functions; acts as an adaptor that helps Rsp5p recognize and ubiquitinate misfolded, cytosolic proteins after heat shock; critical for determining cell size at Start as a function of growth rate; involved in protein translocation across membranes; forms cytotoxic amyloidogenic-like structures in vitro; DnaJ family member; chimeric protein in which the human p58IPK J domain replaces the yeast Ydj1p J domain can complement yeast ydj1 mutant