Heat shock proteins (HSP) are a large and complex family of proteins that play important roles in cellular function and survival. In previous studies, cDNA for a 45 kD human HSP (HDJ-2) was cloned and shown to be homologous to DNA-J, a bacterial HSP [F.M. Ausubel, R. Brent, R. E. Kingston, D.D. Moore, J.G. Seidman, J.A. Smith, K. Struhl, Current Protocols in Molecular Biology, John Wiley and Sons, New York, 1997; A. Chellaiah, A. Davis, T. Mohanakumar, Cloning of a unique human homologue of the Escherichia coli DNAJ heat shock protein, Biochim. Biophys. Acta 1174 (1993) 111-113]. We have also shown that the expression of HDJ-2 is highly elevated in kidney allograft biopsies of kidneys undergoing rejection [Y.G. Alevy, D. Brennan, S. Durriya, T. Howard, T. Mohanakumar, Increased expression of the HDJ-2 heat shock protein in biopsies of human rejected kidneys, Transplantation 61 (1996) 963-967]. Because of the potential importance of HDJ-2 to disease pathogenesis, we carried out studies to characterize the structure and regulation of HDJ-2. Polyclonal and monoclonal antibodies that recognize recombinant HDJ-2 were prepared and used to localize its cellular expression. HDJ-2 was found to be farnesylated but not glycosylated. This HSP was ubiquitously expressed in all of the cell types we analyzed and was localized throughout the cytoplasm and around the nuclear membrane. However, upon heat shock it migrated to the Golgi, nucleolus, and the nuclear membrane. Northern blot analysis revealed two mRNA transcripts whose synthesis was not affected by heat shock. In addition, Western blot analysis showed that expression of HDJ-2 was also not affected by heat shock. Thus, our study shows the characterization of a HSP which, because of its migration pattern upon heat shock, is an excellent candidate for a protein chaperon.