Promoters of the phycocyanin gene clusters of the cyanobacterium Synechococcus sp. strain PCC 7942.

The cyanobacterium Synechococcus sp. strain PCC 7942 has duplicated phycocyanin subunit gene clusters cpcB1A1 and cpcB2A2, which are identical to each other and to those of Synechococcus sp. strain PCC 6301 (Anacystis nidulans). Nucleotide sequences of the 428 and 286 bases of the 5' non-coding regions of the cpcB1A1 and cpcB2A2 clusters, respectively, of strain PCC 7942 were identical to those of strain PCC 6301. As in strain PCC 6301, cpcB1A1 yielded two major transcripts of 1.4 and 1.3 kb and cpcB2A2 yielded a single transcript of 1.3 kb in strain PCC 7942. Thus, the structure and expression of cpcBA gene clusters in the two strains are essentially the same. Using bacterial luciferase encoded by luxAB as a reporter, cpcB1A1 was shown to have two promoters corresponding to the two major transcripts. Luminescence from the Synechococcus reporter strains carrying the fusions of the cpcBA promoters to luxAB showed circadian oscillation. Similar to the promoter of psbA1 encoding the D1 protein of PSII, the two cpcB1A1 promoters and the cpcB2A2 promoter showed the peak of activity at the end of the subjective day and the trough at the end of the subjective night.