HETEROLOGOUS ASSEMBLY AND RESCUE OF STRANDED PHYCOCYANIN SUBUNITS BY EXPRESSION OF A FOREIGN CPCBA OPERON IN SYNECHOCYSTIS SP STRAIN-6803

Light harvesting in cyanobacteria is performed by the biliproteins, wh ich are organized into membrane-associated complexes called phycobilis omes. Most phycobilisomes have a core substructure that is composed of the allophycocyanin biliproteins and is energetically linked to chlor ophyll in the photosynthetic membrane, Rod substructures are attached to the phycobilisome cores and contain phycocyanin and sometimes phyco erythrin. The different biliproteins have discrete absorbance and fluo rescence maxima that overlap in an energy transfer pathway that termin ates with chlorophyll. A phycocyanin-minus mutant in the cyanobacteriu m Synechocystis sp, strain 6803 (strain 4R) has been shown to have a n onsense mutation in the cpcB gene encoding the phycocyanin beta subuni t. We have expressed a foreign phycocyanin operon from Synechocystis s p, strain 6701 in the 4R strain and complemented the phycocyanin-minus phenotype, Complementation occurs because the foreign phycocyanin alp ha and beta subunits assemble with endogenous phycobilisome components , The phycocyanin alpha subunit that is normally absent in the 4R stra in can be rescued by heterologous assembly as well, Expression of the Synechocystis sp. strain 6701 cpcBA operon in the wild-type Synechocys tis sp, strain 6803 was also examined and showed that the foreign phyc ocyanin can compete with the endogenous protein for assembly into phyc obilisomes.