The blue-colored linker polypeptide L55 is a fusion protein of phycobiliproteins in the cyanobacterium synechocystis sp. strain BO 8402

Coordinate up-regulation of carotenoid biosynthesis as a response to light stress in Synechococcus PCC7942

Carotenoid biosynthesis is up-regulated by strong light in the cyanobacterium Synechococcus. By blocking off the pathway at the level of phytoene conversion, light-dependent accumulation of phytoene was observed. Real-time PCR studies demonstrated that four genes of the carotenogenic pathway are under transcriptional control. These were the genes encoding phytoene synthase, phytoene desaturase, zeta-carotene desaturase and beta-carotene hydroxylase. The transcript of the first three follow a similar kinetics, whereas the transcript of beta-carotene hydroxylase increased much faster upon transfer to high light. Promoter activities were determined with transcriptional fusions to chloramphenicol acyltransferase as reporter enzyme. The activity of the promoter of the phytoene desaturase/synthase operon was higher under strong light.

Thymine at -5 is crucial for cpc promoter activity of Synechocystis sp. strain PCC 6714

The levels of transcripts of the cpc operon were highly reduced in a PD-1 mutant of cyanobacterium Synechocystis sp. strain PCC 6714. This was due to a substitution of C for T that occurred at 5 bp upstream of the transcription initiation site of the cpc operon. Any substitution for T at the -5 position drastically reduced both in vivo and in vitro promoter activity in cyanobacterium Synechococcus sp. strain PCC 7942 but not the in vivo activity in Escherichia coli. This suggests that the requirement of -5T appears to be specific for a cyanobacterial RNA polymerase-promoter combination.

Interference of an apcA insertion with complementary chromatic adaptation in the diazotrophic Synechocystis sp. strain BO 8402

Complementary chromatic adaptation was studied in two unicellular diazotrophic Synechocystis-type cyanobacteria, strains BO 8402 and BO 9201. Strain BO 8402 was isolated from Lake Constance as a mutant lacking phycobilisomes due to an insertion sequence element in the gene apcA, encoding alpha-allophycocyanin. Strain BO 9201 recovered the ability to assemble functional phycobilisomes after a spontaneous excision of the insertion sequence element in apcA. Simultaneously, the strain became able to perform group II complementary chromatic adaptation by regulating the synthesis of phycoerythrin. The two strains had identical phycoerythrin operons, cpeBA, and similar-sized transcripts were formed upon induction by green light. However, in strain BO 8402 the cpeBA transcript level was approx. 20-fold lower than in strain BO 9201. Because strain BO 8402 cannot synthesize allophycocyanin and phycocyanin is sequestered in paracrystalline inclusion bodies, non-assembled phycoerythrin may accumulate inside the cells. It was examined whether non-assembled phycoerythrin or other effects caused by the absence of phycobilisomes, such as a permanently oxidized redox status of the photosynthetic electron transport chain or a distorted ratio of C and N assimilation mediated the repression of cpeBA transcription in strain BO 8402. No such links could be established. We therefore concluded that in these diazotrophic Synechocystis-type cyanobacteria the green light-induced transcription of the cpe operon directly required a functional apc operon.

A phycocyanin-deficient mutant of synechocystis PCC 6714 with a single-base substitution upstream of the cpc operon

The structure and expression of the cpc operon encoding phycocyanin subunits and linker polypeptides in a phycocyanin-deficient mutant (PD-1) and the wild-type of Synechocystis PCC 6714 were analyzed. The results of sequence and Northern blot analyses of the wild type indicate that the cpc operon consists of cpcB, cpcA, cpcC1, cpcC2 and cpcD, in that order. The levels of the transcripts in PD-1 were one-tenth to one-sixth as high as those in the wild type. In the PD-1 genome, a single-base substitution of C for T has occurred at base 259 upstream of the translational initiation codon of cpcB (at three bases downstream of the putative -10 region). To evaluate the in vivo transcription activities of these promoters in a cyanobacterium, we constructed vectors for the transformation of Synechococcus PCC7942, pANY1 and pANY2, which contain the upstream region of cpcB of the wild type (pANY1) or PD-1 (pANY2) and the promoter-less luxAB fusion. The bioluminescence of the transformants with pANY2 was one-tenth to one-sixth as high as that with pANY1. The coincidence of the results of Northern analysis and the promoter assay shows that the phycocyanin deficiency of PD-1 is due to the single-base substitution in the upstream region of the cpc operon.