Factors affecting the circadian degradation of COP23 in Synechococcus RF-1

The circadian rhythm of COP23, a protein located in the cell membrane of Synechococcus RF-1, was regulated by a circadian synthesis rhythm and a circadian degradation rhythm. The circadian synthesis rhythm was controlled mainly at the transcriptional level (Chen et al., 1996). For the circadian degradation rhythm, some factors were responsible for COP23 degradation. The addition of chloramphenicol to the cultures prevented COP23 degradation, so new protein(s) synthesis before the decline of COP23 must be essential for COP23 degradation. When EGTA was added to the Synechococcus RF-1 cultures before COP23 degradation, the decline of COP23 was prevented. Thus, extracellular Ca2+ was required for the circadian degradation of COP23. However, the addition of EGTA did not affect the synthesis rhythm of COP23. Light was also needed for COP23 degradation. Comparing the light spectra, blue light is more effective for COP23 degradation than white or red light. Phosphorylation could not be detected in vivo or in vitro before COP23 degradation. Thus, COP23 degradation seemed not to be attributed to its phosphorylation.