Post-transcriptional Control of Nitrate Reductase Formation in Green Algae

Abstract
Cycloheximide (2·0 μg ml−1) inhibits the incorporation of [14C]phenylalanine and [14C]adenine into insoluble compounds in Ankistrodesmus braunii. 6-Methylpurine (1·0 mM) inhibits only the incorporation of [14C]adenine and it is concluded that it inhibits RNA synthesis. When ammonium-grown cells of Ankistrodesmus or Chlorella are nitrogen-starved or when ammonium-grown cells of Dunalitlla are resuspended in nitrate medium, the appearance of nitrate reductase in these organisms is not inhibited by 6-methylpurine. The appearance of nitrate reductase activity in Ankistrodesmus or Chlorella is inhibited by 6-methylpurine when ammonium-grown organisms are preincubated with this substance for 1-2 h before nitrogen starvation. It is concluded that cells growing with ammonium and lacking nitrate reductase activity nevertheless contain preformed mRNA for nitrate reductase synthesis.

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