GENE STRUCTURE OF A CHLOROPHYLL A C-BINDING PROTEIN FROM A BROWN ALGA- PRESENCE OF AN INTRON AND PHYLOGENETIC IMPLICATIONS/

A Laminaria saccharina genomic library in the phage EMBL 4 was used to isolate and sequence a full-length gene encoding a fucoxanthin-chloro phyll a/c-binding protein. Contrary to diatom homologues, the coding s equence is interrupted by an intron of about 900 bp which is located i n the middle of the transit peptide. The deduced amino acid sequence o f the mature protein is very similar to those of related proteins from Macrocystis pyrifera (Laminariales) and, to a lesser extent, to those from diatoms and Chrysophyceae. Seven of the eight putative chlorophy ll-binding amino acids determined in green plants are also present. Al ignments of different sequences related to the light-harvesting protei ns (LHC) demonstrate a structural similarity among the three transmemb rane helices and suggest a unique ancestral helix preceded by two beta -turns. The beta-turns are conserved in front of the second helices of the chlorophyll a/c proteins more so than in chlorophyll a/b proteins . Phylogenetic trees generated from sequence data indicate that fucoxa nthin- chlorophyll-binding proteins diverged prior to the separation o f photosystem I and photosystem II LHC genes of green plants. Among th e fucoxanthin-containing algae, LHC I or II families could not be dist inguished at this time.