The heat shock proteins (hsps) are a large family of proteins that participate in a wide variety of important cellular processes. The best studied of these processes are translocation across endoplasmic reticular and mitochondrial membranes and protein folding and assembly reactions within the cytoplasm and within the organellar matrices. The hsps of the protozoan parasite Trypanosoma cruzi have proven to be of interest for a number of reasons. First, they are among the most immunogenic proteins of the parasite and T. cruzi-infected individuals mount strong humoral and cellular immune responses to these hsps that likely contribute both to parasite resistance and to disease pathogenesis. Second, the hydrolysis of ATP by hsps drives the protein folding process and some trypanosome hsps have ATPase activities that are much greater than those of their mammalian counterparts. Third, the mitochondrial member of the 70 kDa family of T. cruzi, mt-hsp70, is concentrated in the kinetoplast, a submitochondrial structure that contains the mitochondrial DNA nucleoid and defines the species of the kinetoplastid order. This, and several other findings that will be presented below, suggests that mt-hsp70 is involved in mitochondrial nucleic acid metabolism, a function of hsp70 family members not previously studied in eukaryotic cells. Over the past several years, we have molecularly cloned and partially characterized most of the major hsps of T. cruzi and have studied various aspects of their biology--immunity, genetics, expression, subcellular localization and biochemistry. During this period, it was discovered by others that a family of assistants exists that serves to modulate hsp70 activity, the substrate binding and ATPase activities in particular. Like the hsp70s, these assistants, the DnaJ proteins, are found in every cellular compartment and are critical for the proper functioning of their hsp70 partners. That work serves as the foundation for this research proposal, which begins with general studies of the T. cruzi DnaJ family and then focusses on the biology of the most interesting and unique of the T. cruzi hsp--those found in the mitochondrion. We propose experiments to address these issues in a comprehensive, five year research project, the Specific Aims of which are as follows: 1. Characterization of the T. cruzi DnaJ family. 2. Identification and molecular cloning of T. cruzi mt-hsp70 and mt-DnaJ partner/substrate proteins. 3. Biochemical studies of T. cruzi DnaJ, hsp70 and GrpE proteins. 4. Structure-function analysis of mitochondrial hsps.