The molecular chaperone family of 90kDa heat shock proteins (Hsp90) is a highly conserved protein family that plays an important physiological role. Hsp90 is best known for its association with signal transduction processes. Tumor necrosis factor receptor-associated protein 1 (TRAP1) is a recently cloned homolog of Hsp90. Like Hsp90, TRAP1 is associated with numerous proteins that are involved in multiple pathways. Data indicates that TRAP1 is a mitochondrial matrix protein: it is localized in mitochondria of mammalian cells and contains a mitochondrial targeting presequence.