RIBOSOMES OF ACETABULARIA MEDITERRANEA

1. 1. Whole homogenates of [3H]uridine-labelled Acetabularia mediterranea contain two major species of radioactive ribosomal particles, sedimenting at approx. 50 and 30 S. These particles contain, respectively, high and low molecular weight ribosomal RNA species. The 70-S free ribosomal monomers occur as a minor radioactive component. 2. 2. Anucleate fragments of Acetabularia are capable of incorporating [3H]uridine into the ribosomes of both the chloroplast and non-chloroplast fractions. The newly formed ribosomes are found almost exclusively as polyribosomes and 50- and 30-S particles. In the non-chloroplast fraction, both the 50 and 30 units are probably synthesized independently from each other. Sucrose gradient centrifugation shows no difference between the sedimentation characteristics of the ribosomes from the chloroplast and non-chloroplast fractions. 3. 3. Significant amounts of chloroplast ribosomes, occurring mainly as 50- and 30-S particles, were isolated from Acetabularia. 4. 4. The incorporation of [3H]uridine into contaminating micro-organisms was found to be negligible as compared to the incorporation into the algae. © 1969.