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[en] The heat-shock response of Euglena gracilis was studied by pulse-labeling cells with [³⁵S] sulfate at both the normal growth temperature (21 degree C) and an elevated temperature (36 degree C). Analysis of the labeled proteins by polyacrylamide gel eletrophoresis 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 (p70) 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

[en] The heat shock response of Euglena gracilis was studied and the proteins synthesized were identified. Cells were pulse-labeled with [³⁵S] sulfate at 21 degrees C or 36 degrees C and the proteins synthesized were analyzed by acrylamide gel analysis. The rate of synthesis of at least 4 major and 6 minor polypeptides, ranging from 25 Kd to 116 Kd increased in both light and dark grown cultures. Two polypeptides, 68 Kd and 69 Kd, were found to cross-react by immunoblot analysis with monoclonal antibodies raised against human 72 and 73 Kd heat shock proteins. Both the 68 Kd and 69 Kd proteins were expressed at 21 degrees C; however, the synthesis of only the 68 Kd protein increased at 36 degrees C. The 68 Kd heat inducible protein was present in the cytoplasm and nucleus, but not the chloroplast, in cells grown at 21 degrees C or exposed to 36 degrees C. Both 68 Kd and 69 Kd proteins copurified during ATP-agarose affinity chromatography. Preliminary evidence indicates that the 68 Kd protein is phosphorylated in the presence of Ca⁺⁺ and these proteins exhibit ATPase activity