Abstract
A circadian clock resetting protein Pex in the cyanobacterium Synechococcus elongatus PCC 7942 accumulates dark condition and regulates the phase and period of the rhythm. Pex binds to the promoter of the clock essential gene kaiA, whose protein KaiA accelerates the phosphorylation of KaiC protein and shortens the circadian cycle. Then, Pex represses the expression of the clock gene. An alpha helix and a positively charged loop between two beta sheets in Pex is essential to bind the promoter in vitro and the in vivo period regulation. Here, we examined molecular weight of Pex in vivo by gel-filtration method and determined as 25 kD in size, suggesting Pex dimer because its monomer shows 13.1 kDa in SDS polyacrylamide gel. Then, we also show the importance of the dimer formation by using bioluminescence rhythm monitoring method and several reporter strains expressing an amino acid replaced Pex protein.
