Abstract
Luciferase genes have been used as a tool to monitor circadian rhythms of promoter activity in many organisms. We here tried to monitor circadian rhythmicities in the activities of clock gene promoters in Chlamydomonas. The promoter regions of the clock genes ROC15 and ROC75 were fused to a codon-optimized firefly luciferase coding sequence. Since ROC15 and ROC75 mRNA levels oscillate with an 8-hour phase-angle-difference, we expected that bioluminescence rhythms of the two reporters oscillate with a similar phase-angle-difference. Surprisingly, however, bioluminescence rhythms of ROC15 and ROC75 reporters oscillated with essentially the same phase angles. Do activities of the promoter regions not reflect in luciferase gene expressions? The circadian rhythms of luciferase mRNA level in the ROC15 and ROC75 reporter strains oscillated with a phase-angle-difference similar to that of endogenous ROC15 and ROC75 mRNAs, suggesting that circadian rhythmicities of luciferase reporters are regulated at posttranscriptional steps in Chlamydomonas.
