English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

The fact that anucleate fragments of Acetabularia mediterranea are capable of regeneration and morphogenesis and of specific protein synthesis has been known for many years." 2 The information needed for these processes obviously comes from the nucleus and must be stored for a considerable time in the cytoplasm: this can be most readily explained in molecular terms by assuming that the nucleus produces messenger ribonucleic acids (mRNA's), which ma} well remain in a stable and active form in the anucleate cytoplasm for several weeks. This hypothesis, which has been presented and discussed several times by one of US,' 4 is supported by a number of indirect experiments: the effects of actinomycin,5 6 ribonuclease,7 and localized UV radiation8 have been found to be those one would expect if one assumes the presence, at the apex of the stalk, of stable RNA molecules originating from the nucleus. More direct evidence comes from autoradiography8 I which shows that precursors for RNA synthesis (adenine, for instance) are at first incorporated into the nucleolus; in pulse experiments, the labeled nuclear RNA migrates into the cytoplasm, where it becomes distributed along a decreasing apico-basal gradient. Regarding total RNA synthesis in anucleate fragments, we should mention the results of Naora et al."0 and of Schweiger and Bremer:11 the former found that in anucleate fragments of Acetabularia there is a synthesis of "chloroplastic" RNA, and a parallel decrease of the RNA fractions (presumably mostly ribosomal RNA) which remain in the supernatant after centrifugation of the chloroplasts. Schweiger and Bremer" found that anucleate fragments can synthesize considerable amounts of RNA if the algae are kept in darkness for a few days before section. These two sets of experiments suggested that the presence of chloroplasts might be an important factor in the study of RNA metabolism in Acetabularia. In fact, isolated chloroplasts contain DNA12 1" that can synthesize RNA14 15 molecules, the nature of which remains unknown. The fact that this in vitro RNA synthesis is partially inhibited by treatment of the isolated chloroplasts with actinomycin suggests that chioroplastic DNA is the template for the synthesis of these RNA molecules. In order to clarify this situation, we have studied the following points: (1) the base composition of the RNA's present in the nucleolus, the nuclear sap, the apical (capable of regeneration) and basal (incapable of regeneration) parts of the stalk, whole chloroplasts, and ribosomes isolated from the chloroplasts; (2) the base composition of gametic DNA; (3) the behavior of ribosomes and

Base composition and metabolism of various RNA fractions in Acetabularia mediterranea.