Chloroplast ribosomes in the proplastids of Euglena gracilis

Abstract

1. 1. Density gradient centrifugation in zonal rotors yielded small quantities of chloroplast-like ribosomal subunits in dark-grown Euglena gracilis. Like the chloroplast particles from photoheterotrophically grown Euglena, these subunits were of the 30- and 50-S type and contained a chloroplast-specific rRNA component of 0.60 (± 0.02) · 10 6 daltons and a specific break-down product of 0.78 (± 0.03) · 10 6 daltons. 2. 2. The 30- and 50-S subunits isolated from dark-grown cells were enriched in crude preparations of proplastids, but could not be detected either in an aplastidic mutant or from mitochondrial preparations. 3. 3. From these observations we infer that Euglena gracilis contains small amounts of fully formed chloroplast ribosomal subunits probably localized in the proplastid.