Separation and partial characterization of chloroplast and cytoplasmic ribosomes from Euglena gracilis

Chloroplast and cytoplasmic ribosomes from Euglena graciliswere separated by centrifugation in zonal rotors. The particleswere characterized by their sedimentation rates as well as bytheir RNA components. Total extracts from green cells contained30S, 55S and 89S particles or their aggregates, depending uponthe Mg⁺⁺ concentration. Extracts from fractions enriched forchloroplasts contained essentially 30S and 55S particles, whilethe supernatant (obtained after sedimentation of the chloroplasts)contained predominantly 89S particles or aggregates of cytoplasmicribosomes. The 30S and 55S ribosomes contained RNA componentswhich were unique and distinct from those of the cytoplasmicribosomes. We were unable to detect 70S particles from the chloroplastpreparations. Under our conditions, chloroplast extracts yielded30S and 55S subunits or a series of rapidly sedimenting particles,possibly polysomes. Despite a variety of extraction techniques,we were unable to detect 70S particles from the chloroplasts. ¹This study was supported in part by grant No. HD 01787 fromthe U. S. Public Health Service. Journal paper of the New JerseyAgricultural Experiment Station (Received December 3, 1969; )