HSP40, also known as HDJ1 (9), is a basic mammalian 40kD heat shock protein which is homologous to the bacterial heat shock protein, DnaJ, and yeast DnaJ-related proteins such as SCJ1, Sec63/Npl1, YDJ1 and SIS1 (1,2,3,4). Like many heat shock proteins, HSP40 is inducible by heat, transient metals and azetidine carboxylic acid in mammalian and avian cells (2). In heat shocked HeLa cells, HSP40 translocates rapidly from the cytoplasm to the nucleus and nucleoli; an intracellular pattern similar to HSC70/HSP70, the mammalian homologues of the bacterial heat shock protein, DnaK (1). This suggests that HSP40 colocalizes with HSP70 and together they repair denatured proteins in the nuclei and nucleoli of heat shocked cells (1). This is analogous to the functions of bacterial DnaJ and DnaK which have been shown to act together in dissociating the bacteriophage lambda protein complexes (5,6) and monomerizing the Rep A dimer (7).