cpmA, a gene involved in an output pathway of the cyanobacterial circadiansystem

We generated random mutations in Synechococcus sp. strain PCC 7942 to look for genes of output pathways in the cyanobacterial circadian system. A deri vative of transposon Tn5 was introduced into the chromosomes of reporter st rains in which cyanobacterial promoters drive the Vibrio harveyi luxAB gene s and produce an oscillation of bioluminescence as a function of circadian gene expression. Among low-amplitude mutants, one mutant, tnp6, had an inse rtion in a 780-bp open reading frame. The tnp6 mutation produced an altered circadian phasing phenotype in the expression rhythms of psbAI::luxAB, psb AII::luxAB, and kaiA::luxAB but had no or little effect on those of psbAIII ::luxAB, purF::luxAB, kaiB::luxAB, rpoD2::luxAB, ndhD::luxAB, and conII::lu xAB. This suggests that the interrupted gene in tnp6, named cpmA (circadian phase modifier), is part of a circadian output pathway that regulates the expression rhythms of psbAI, psbAII, and kaiA.