STUDIES ON RNA METABOLISM IN ACETABULARIA MEDITERRANEA .2. LOCALIZATION AND STABILITY OF RNA SPECIES - EFFECTS ON RNA METABOLISM OF DARK PERIODS AND ACTINOMYCIN D

1. 1. Slowly labelled 15-S RNA of Acetabularia is synthesized in the chloroplasts. The predominant radioactive species of mitochondria and other cellular constituents is a 5-S type of RNA. 2. 2. The exposure of plants to long dark periods markedly inhibits the incorporation of RNA precursors into chloroplast RNA. A new RNA species appears in sedimentation profiles following this treatment. 3. 3. The labelling of very young plants results in the retention of the slowly labelled 15-S component after a 35-day chase. Sedimentation profiles of RNA isolated following a 58-day chase are polydisperse, and indicate that the 15-S peak has been split into several fractions. Plants possess caps at this stage. When plants at the same stage of development are labelled, the 15-S component is still the predominantly labelled species. 4. 4. Actinomycin D chase experiments do not result in any changes in the relative proportions of labelled RNA species in whole algae or plant fragments. However, pretreatment with the antibiotic causes the suppression of all RNA fractions with exception of the 5-S component. © 1969.