The protein-synthesizing systems from the cytoplasm and the chloroplasts of Euglena gracilis

Abstract

Chloroplasts from Euglena gracilis, free of contamination by cytoplasmic ribo-somes, promote the incorporation of amino acids into acid-insoluble material. The activity is highly dependent on a Euglena supernatant fraction, an ATP-generating system and transfer RNA. It is inhibited by ribonuclease, puromycin and chloramphenicol. Light produces a marked inhibition of the incorporation by chloroplasts. In the absence of the ATP-generating system, however, the incorporation is stimulated by light. The activity of the chloroplasts is somewhat stimulated by the ribonucleoside triphosphates and inhibited by actinomycin. This is tentatively considered as evidence for DNA-dependent RNA polymerase activity. Ribosomes derived from the chloroplasts are considerably less active than the intact chloroplasts. Their activity is greatly enhanced by the addition of template RNA. The intact chloroplasts are not stimulated by this material. The chloroplast ribosomal unit active in protein synthesis shows a sedimentation value of 60 s. The corresponding value for the cytoplasmic ribosomes is 70 s. The two types of ribosomes also differ markedly with respect to nucleotide composition of the RNA. The cytoplasmic ribosomes, obtained by a procedure similar to that used for the preparation of the chloroplast particles, are not stimulated by template RNA. They are also insensitive to chloramphenicol. A possible correlation between the properties of the two types of ribosomes and the characteristics of chloroplast and cytoplasmic protein synthesis in vivo is suggested.