Studies on Independent Synthesis of Cytoplasmic Ribonucleic Acids in Acetabularia mediterranea

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Abstract
The RNA content of anucleate and nucleate fragments of Acetabularia has been measured. It was found that there is a net synthesis of RNA in nucleate fragments. On the other hand, the RNA content of anucleate fragments did not change significantly after enucleation. Anucleate fragments, however, can readily incorporate C14-labeled adenine, orotic acid, and CO2 into their cytoplasmic RNA. The results of experiments on C14O2 incorporation into the RNA of anucleate and nucleate fragments suggest that there is a mechanism for de novo synthesis of RNA in anucleate cytoplasm. In Acetabularia, 81% of the cytoplasmic RNA is bound to a large granule fraction, consisting mainly of chloroplasts. Even after removal of the nucleus, RNA is synthesized in this "chloroplast" fraction. The chloroplasts are thus a major site of RNA synthesis in the cytoplasm of these algae. Synthesis of "chloro-plastic" RNA, in anucleate fragments, possibly occurs at the expense of the RNA present in other fractions (microsomes and supernatant). 8-Azaguanine stimulates regeneration and cap formation in anucleate fragments and does not inhibit RNA synthesis in these fragments.