The recent availability of the whole genome of sp. linker. The second one (SYNW1989) has a more classical size (300 residues) and is also an MpeC paralog. A biochemical analysis exposed that like MpeC these two novel linkers were both chromophorylated with phycourobilin. Our data suggest that they may be both connected (partly Skepinone-L or totally) with phycoerythrin Skepinone-L II Skepinone-L and we propose to name SYNW2000 and SYNW1989 MpeD and MpeE respectively. We further show that acclimation of phycobilisomes to high light prospects to a dramatic reduction of MpeC whereas the two novel linkers are not significantly affected. Models for the organization of the rods are proposed. Phycobilisomes (PBSs) are the major light-harvesting systems used by cyanobacteria and reddish algae. This type of photosynthetic antenna consists of a macrocomplex composed of chromophorylated proteins designated phycobiliproteins (PBPs). These are organized like a core connected with photosystems and generally surrounded by six peripheral rods (for a review observe e.g. research 37). PBSs are very variable in structure and pigment composition and this offers allowed cyanobacteria to colonize environments showing a great diversity in terms of light amount and quality. The PBSs of open-ocean cyanobacteria are among the most complex ones explained to date since they possess four types of constitutive PBPs: allophycocyanin (APC) phycocyanin (Personal computer) and two forms of phycoerythrin PEI and PEII the second option being specific for these organisms. Each PBP covalently binds one or two types of tetrapyrrole chromophores (designated phycobilins) to cysteinyl residues via a thioether relationship. PEI and PEII bind both phycourobilin (PUB; absorption maximum [possesses three linker proteins: CpeC -D and -E (12). Light quality and amount are among the major factors influencing the composition of PBSs. In spp. (32 46 Changes in photon fluxes also have an effect within the structure of PBSs. Marine cyanobacteria primarily respond to high light stress by decreasing the content of PBSs per cell (20 38 This decrease is mainly attributable to a reduction of the surface of thylakoid membranes (19). In freshwater cyanobacteria and rhodophytes it has been shown the PBS rods may also shorten after cells have been transferred from low to high light conditions (4 23 26 27 36 However whether this trend also happens in marine and to what degree have been little studied so far (38). With this study we used a combination of genomic and biochemical analyses to study the composition of PBSs of the marine strain WH8102 and structural changes happening in PBSs as a result of photoacclimation. This strain is characterized by its very high PUB/PEB percentage standard of open-ocean populations of strains have been extensively analyzed through an excellent series of papers by A. N. Glazer and coworkers (observe e.g. recommendations 29-31 and 47-49) the availability of the whole genome of sp. strain WH8102 offers allowed us to have a global look at of the organization of PBS genes. This analysis exposed a number of novelties including the presence of two novel genes encoding putative PE-associated linker polypeptides. Using a biochemical approach we have been able to confirm the presence of these linkers in the PBSs and to characterize some Rabbit polyclonal to ANGEL2. of their properties including their probable localization within the PBS rods. MATERIALS AND METHODS Genomic analysis. The methods utilized for sequencing and modeling the genome of sp. strain WH8102 (GenBank/EMBL accession quantity “type”:”entrez-nucleotide” attrs :”text”:”NC_005070″ term_id :”33864539″ term_text :”NC_005070″NC_005070) have been described elsewhere (33). Results from the automated annotation were checked manually and completed by BlastP analyses (2) of the genome data lender with individual PBS proteins known from additional marine spp. or freshwater cyanobacteria. Alignments of linker polypeptides were made using ClustalW (43) and processed by hand. Tradition conditions. The axenic marine sp. clone WH8102 was produced at 23 ± 1°C in 8 liters of polycarbonate tradition flasks (Nalgene) comprising 0.2 μm filtered PCR S-11 medium (34). Cultures had been steadily acclimated for at least four weeks to a variety of constant white irradiances (from 15 to 250 μmol of photons · m?2 · s?1) supplied by 10 daylight 865/36W fluorescent pipes (Mazdafluor Prestiflux) and different combinations of thickness and/or Skepinone-L diffusion filter systems.