The orange carotenoid protein of Synechocystis PCC 6803.

A water soluble protein with the carotenoid 3'-hydroxyequinenone bound to it has been purified from the cyanobacterium Synechocystis PCC 6803. Based on partial amino acid sequencing of the protein, oligonucleotides were synthesized and used as primers for PCR to obtain a substantial fragment of the gene. This DNA was sequenced and the sequence data and the size of the protein indicate that the protein is encoded by gene slr 1963 in the Kazusa DNA sequence data bank containing the Synechocystis 6803 genome. This protein is very similar to 3'-hydroxyechinenone proteins found in several other cyanobacteria but it shows very little resemblance in its amino acid or gene sequence to other carotenoid binding proteins. The protein binds 1-2 molecules of 3'-hydroxyechinenone and is slowly cleaved by proteases in the cell extract to give a molecule of approximately half the original mass which retains the carotenoid and which shows a striking change in color.