CLONING AND NUCLEOTIDE-SEQUENCE OF A CDNA-ENCODING A MAJOR FUCOXANTHIN, CHLOROPHYLL A C-CONTAINING PROTEIN FROM THE CHRYSOPHYTE ISOCHRYSIS-GALBANA - IMPLICATIONS FOR EVOLUTION OF THE CAB GENE FAMILY/

We investigated the primary structure of a cDNA encoding a light-harve sting protein from the marine chrysophyte Isochrysis galbana. Antibodi es raised against the major fucoxanthin, chlorophyll ale-binding light -harvesting protein (FCP) of I. galbana were used to select a cDNA clo ne encoding one of the FCP apoproteins. The nucleic acid and deduced a mino acid sequences reveal conserved regions within the first and thir d transmembrane spans with Chi a/b-binding proteins and with FCPs of a nother chromophyte. However, the amino acid identity between I. galban a FCP and other cab genes of FCPs is only ca. 30%. Phylogenetic analys es demonstrated that the FCP genes of both diatoms and chrysophytes se quenced to date are more closely related to cab genes encoding LHC I, CP 29, and CP 24 of higher plants than to cab genes encoding LHC II of chlorophytes. We propose that LHC I, CP 24 and CP 29 and FCP might ha ve originated from a common ancestral chi binding protein and that the major LHC II of Chl a/b-containing organisms arose after the divergen ce between the chromophytes and the chlorophytes.