Structure Volume 13, Issue 5, May 2005, Pages 735–741
Recent Cyanobacterial Kai Protein Structures Suggest a Rotary Clock
Jimin Wang
Under an Elsevier user license
Source/Fonte: Rolex
Introduction
The cyanobacterial circadian oscillator, which controls internal daily periodicity, consists of three Kai proteins, KaiA, KaiB, and KaiC, in its oscillation feedback loop (Ishiura et al., 1998). KaiC is a negative element of the loop, repressing the expression of its own KaiBCand other global genes; KaiA is a positive element, releasing the repression. The discovery of a bacterial clock unexpectedly breaks the paradigm of biological clocks, because rapid cell division and chromosome duplication in bacteria occur within one circadian period ( Kondo et al., 1994 and Kondo et al., 1997). In fact, these cyanobacterial oscillators in individual cells have a strong temporal stability with a correlation time of several months (Mihalcescu et al., 2004). The cyanobacterial circadian system is the simplest of all clock forms and possesses the same three levels of organizations as do all other biological clocks: the generation of oscillation in its feedback loop, amplification of oscillating signals for gene expression, and coordination with daily environmental events (Harmer et al., 2001). Upon reviewing recent biochemical and structural studies, I shall provide insights into the inner working of this bacterial clock and provide evidence for a striking similarity between the Kai clock and the F1-ATPase system.
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