HSP70 PROTEINS, SIMILAR TO ESCHERICHIA-COLI DNAK, IN CHLOROPLASTS AND MITOCHONDRIA OF EUGLENA-GRACILIS

The heat-shock response of Euglena gracilis was studied by pulse-labeling cells with [35S]sulphate at both the normal growth temperature (21°C) and an elevated temperature (36°C). Analysis of the labeled proteins by polyacrylamide gel electrophoresis indicated that the rate of synthesis of at least 3 major and 15 minor polypeptides increased in cells grown at the higher temperature. Three of the proteins appear to be immunologically related to the ubiquitous ~70-kDa heat-shock protein (Hsp70) family. One protein of 68 kDa was found in the cytoplasm (P68(cyt)) and was the major heat-shock protein in Euglena gracilis. Two other proteins, 68 and 70 kDa, were localized in mitochondria (P68(mit)) and chloroplasts (P70(chl)), respectively, and they crossreacted with a polyclonal antibody raised against the Escherichia coli heat-shock protein DnaK. Like DnaK, P68(mit) and P70(chl) could be phosphorylated in vitro with (γ-32P]ATP in a reaction that was stimulated by Ca2+. A protein with characteristics similar to those of P70(chl) was also found in chloroplasts isolated from maize and spinach.