THE 38 KDA CHLOROPHYLL-A CHLOROPHYLL-B PROTEIN OF THE PROKARYOTE PROCHLOROTHRIX-HOLLANDICA IS ENCODED BY A DIVERGENT PCB GENE/

The chlorophyll (Chi) a/b proteins of the photosynthetic prokaryotes a ppear to have evolved by gene duplication and divergence of the core C hi a antenna family, which also includes CP43 and CP47 and the iron-st ress induced Chi a-binding IsiA proteins. We show here that Prochlorot hrix hollandica has a cluster of three pcb (prochlorophyte chlorophyll b) genes which are co-transcribed. The major antenna polypeptides of 32 and 38 kDa are encoded by pcbA and pcbC respectively. The pcbC gene is significantly divergent from the other two and may have originated by a gene duplication independent of the one that led to isiA and the other prochlorophyte pcb genes. The distant relatedness of the three prochlorophyte genera implies that not only the ability to make Chl b and use it for light-harvesting arose independently in the three linea ges, but also that the pcb genes may have arisen as the result of inde pendent gene duplications in each lineage.