Template and ribosomal ribonucleic acids associated with the chloroplasts and the cytoplasm of Euglena gracilis

Abstract

Zone centrifugation of the RNA derived from the cytoplasm of Euglena gracilis produces one broad peak (19 s). The chloroplast RNA yields two components (14 s and 19 s). The two chloroplast components appear to have the same nucleotide composition, which is sharply different from that of the cytoplasmic 19 s material. Template RNA, studied through its ability to stimulate preincubated Escherichia coli ribosomes, appears as two well-defined sedimentation peaks (11 to 13 s and 22 s). Similar sedimentation values for template RNA were obtained with chloroplast and cytoplasmic RNA, but the proportion of the heavy and light components was markedly different in the two preparations. The chloroplasts contain a considerably greater amount of template RNA than does the cytoplasm. It is also higher than that of Esch. coli. Lysis of the chloroplasts results in a separation of part of this material from the ribosomes. This template RNA can be recovered in the 100,000 g supernatant fraction of the lysed chloroplasts. The partially depleted chloroplast ribosomes are dependent on added template RNA for their amino-acid-incorporating activity. The cytoplasmic ribosomes, which are considerably more active than the chloroplast particles, contain much less template RNA. Furthermore,a preincubation of the cytoplasmic ribosomes which produces a partial dependency on added RNA templates fails to reduce their template RNA content. The results indicate that ribosomes from various sources differ with respect to their interaction with endogenous template RNA. A possible regulatory role for the ribosomes in the process of protein synthesis is suggested.