Isolation and characterization of a gene for a major light-harvesting polypeptide from Cyanophora paradoxa

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Abstract
Antibodies raised against mixtures of phycobilisome polypeptides from the eukaryotic alga Cyanidium caldarium were used in an immunological screen to detect expression of phycobiliprotein genes in an Escherichia coli library containing segments of plastid (chloroplast, cyanelle) DNA from another eukaryotic alga, C. paradoxa. The 4 candidate clones obtained were mapped by restriction analysis and were overlapping. The clone with smallest insert (1.4 kilobases) was partially sequenced and a coding region similar to the carboxyl terminus of the phycobiliprotein subunit .beta.-phycocyanin was found. The coding region for the .beta.-phycocyanin gene in C. paradoxa was mapped to the small single copy region on the cyanelle genome, and its orientation was determined. A short probe unique to a conserved chromophore binding site shared by at least 2 phycobiliprotien subunits has now been generated from the carboxyl terminus of the .beta.-phycocyanin gene. This probe may be useful in identifying specific phycobiliprotein subunit genes, .beta.-phycocyanin, .beta.-phycoerythrocyanin, and possibly .beta.-phycoerythrin, in other eukaryotic algae and in prokaryotic cyanobacteria.