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Light-stimulated Production of a Chloroplast-localized System for Protein Synthesis in Euglena gracilis¹

^a Biology Division, Oak Ridge National Laboratory, and The University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences, Oak Ridge, Tennessee 37830

Chloroplasts and proplastids isolated respectively from autotrophic and dark-adapted cells of Euglena gracilis strain Z incorporated ¹⁴C-L-leucine into protein. In each case the incorporation was inhibited by chloramphenicol (50% inhibition at about 5 µg/ml for chloroplasts and 30 µg/ml for proplastids), but not appreciably by cycloheximide at concentrations up to 200 µg/ml. Chloroplasts from autotrophic cells incorporated leucine into protein at rates of about 10 pg leucine per mg RNA in one minute, but isolated proplastids were only 5 to 10% as active. When dark-adapted cells were illuminated there was little increase in the activity of the chloroplast fraction during the first 12 hr. Between 12 and 24 hr, when there was a rapid increase in the rate of synthesis of chlorophyll, the capacity of the chloroplast fraction for protein synthesis increased markedly. Suppression of the formation of a chloroplast-localized system for protein synthesis by treating the cells with chloramphenicol and the lack of such an effect with cycloheximide suggests that certain of the proteins which form part of a functional chloroplast system for protein synthesis are themselves synthesized within the chloroplasts.

³ Fulbright-Hayes Fellow and Visiting Professor at the University of Tennessee-Oak Ridge Graduate School of Biomedical Sciences. On leave from the Plant Physiology Unit, Commonwealth Scientific and Industrial Research Organization Division of Food Preservation, Ryde, and School of Biological Sciences. The University of Sydney, Sydney 2006, Australia.

⁴ Present address: Department of Biochemistry. University of Massachusetts, Amherst, Mass.

¹ Research was jointly sponsored by the National Institute of General Medical Sciences, National Institutes of Health, Grant GM 15595, and by the United States Atomic Energy Commission under contract with the Union Carbide Corporation.