HSP68 - A DNAK-LIKE HEAT-STRESS PROTEIN OF PLANT-MITOCHONDRIA

A 68-kDa heat-stress protein (HSP68) has been purified from cell-suspe nsion cultures of tomato (Lycopersicon peruvianum L.). Antibodies rais ed against HSP68 cross-react with the Escherichia coli heat-stress pro tein DnaK. HSP68 was found to be a hydrophilic, ATP-binding protein. I mmunological analysis of subcellular fractions and immunogold-labellin g of ultrathin sections showed consistently that HSP68 is localized in the mitochondrial matrix. In-vitro translation experiments indicated that HSP68 is synthesized as a precursor protein. Immunoscreening of c DNA libraries from tomato and potato (Solanum tuberosum L.) led to the isolation of corresponding cDNA clones. The deduced amino-acid sequen ces show strong relationships to the DnaK-like proteins from bacteria and organelles of eukaryotic cells. The protein HSP68 is constitutivel y expressed, but its synthesis is increased during heat stress in all cells of higher plantes investigated so far.