Prokaryotic cyanobacteria express robust circadian (daily) rhythms under the control of a central clock. Recent studies shed light on the mechanisms governing circadian rhythms in cyanobacteria and highlight key differences between prokaryotic and eukaryotic clocks. reports deposited research Rhythmic gene-expression patterns Circadian biological clocks are self-sustained biochemical oscillators. Their properties include an intrinsic time constant of approximately 24 hours, temperature compensation (so that they run. | Minireview Global orchestration of gene expression by the biological clock of cyanobacteria Carl Hirschie Johnson Address Department of Biological Sciences Vanderbilt University Nashville TN 37235 USA. E-mail Published 29 March 2004 Genome Biology 2004 5 217 The electronic version of this article is the complete one and can be found online at http 2004 5 4 217 2004 BioMed Central Ltd Abstract Prokaryotic cyanobacteria express robust circadian daily rhythms under the control of a central clock. Recent studies shed light on the mechanisms governing circadian rhythms in cyanobacteria and highlight key differences between prokaryotic and eukaryotic clocks. Rhythmic gene-expression patterns Circadian biological clocks are self-sustained biochemical oscillators. Their properties include an intrinsic time constant of approximately 24 hours temperature compensation so that they run at a period of 24 hours irrespective of temperature and entrainment to daily environmental cycles 1 . Many biological processes are controlled by these clocks including gene expression neuronal activity photosynthesis sleeping and waking and development. Microarray analyses of mRNA expression patterns in eukaryotes have demonstrated that 5-10 of genes exhibit daily rhythms of mRNA abundance. But mRNA abundance is not necessarily comparable with transcriptional activity. For example microarray and promoter-trap experiments in the eukaryote Arabidopsis have demonstrated that only 6 of genes showed rhythms of mRNA abundance 2 whereas about 35 of promoters were rhythmically controlled 3 . These results imply that the promoters of many eukaryotic genes are controlled by the biological clock but that post-transcriptional control mechanisms counterbalance the rhythmic transcriptional activity of some genes so that their mRNA abundances are constant. In prokaryotic cyanobacteria it is not a mere fraction of the total entourage of promoters that is .
