Characterization of polypeptides in Euglena gracilis which are synthesized in a circadian manner.

In vivo labeling of proteins in the unicellular phytoflagellate Euglena gracilis, grown under constant light, with [35S]methionine, gave evidence that three proteins of 17,000, 24,000 and 60,000 M(r) were synthesized rhythmically with a period length of 26 h. The 60,000 M(r) protein was synthesized at the subjective end of the 12 h light phase, while the two smaller proteins of 17,000 and 24,000 M(r) shared a maximum of synthesis at the subjective noon. The rate of synthesis oscillated up to 20-fold when the maxima and minima were compared. By isoelectric focusing, the 24,000 M(r) protein was separated into three distinct spots. When different temperatures between 16 and 27 degrees C were applied, the period length of the circadian synthesis rhythms differed by only 3 to 5 h, indicating that the synthesis rhythms of these proteins were almost temperature compensated. Synthesis of the two smaller peptides was inhibited by cycloheximide but not by chloramphenicol, implying that synthesis occurred at 80S ribosomes. Once synthesized and processed, these two proteins were fairly stable in continuous light for about 120 h, while they were degraded during darkness- although slowly. After cell breakage, these proteins were localized in the pelletable membranous fraction.