DEOXYRIBONUCLEOTIDE SYNTHESIS IN GREEN-ALGAE - CELL-CYCLE FLUCTUATIONOF RIBONUCLEOTIDE REDUCTASE IS ONLY MODERATE IN THE UNICELLULAR, EXSYMBIOTIC GREEN-ALGAE, CHLORELLA SP PBI

The time course of ribonucleotide reductase activity in the green alga e, Chlorella sp, pbi, was investigated in partially synchronous cultur es grown in continuous light. Activity was present at all times, with a slight fluctuation interpreted as induction during the G(1) phase of the cell cycle. This result is in accordance with the regulation of t he enzyme in other eukaryotes but in strong contrast with the marked S phase activity maximum of ribonucleotide reductase in cells of Scened esmus obliquus reported earlier. The latter peak pattern should be reg arded as consequence of a light-dark-regime rather than of the cell cy cle itself.