Characterization of a gene encoding the light-harvesting violaxanthin-chlorophyll protein of Nannochloropsis sp (Eustigmatophyceae)

In contrast to vascular plants, green algae, and diatoms, the major light-h arvesting complex of the marine eustigmatophyte genus Nannochloropsis is a violaxanthin-chlorophyll a protein complex that lacks chlorophylls b and c, The isolation of a single polypeptide from the light-harvesting complex of Nannochloropsis sp, (IOLR strain) was previously reported (Sukenik et al, 1992), The NH2-terminal amino acid sequence of this polypeptide tvas signif icantly similar to NH2-terminal sequences of the light-harvesting fucoxanth in, chlorophyll a/c polypeptides from the diatom Phaeodactylum tricornutum Bohlin, Using polyclonal antibodies raised to the Nannochloropsis light-har vesting polypeptide, a gene encoding this polypeptide was isolated from a c DNA expression library. The deduced amino acid sequence of the Nannochlorop sis violaxanthin-chlorophyll a polypeptide reveals a 36 amino acid preseque nce followed by 173 amino acids that constitute the mature polypeptide. The mature polypeptide has 30%-40% sequence identity to the diatom fucoxanthin -chlorophyll a/c polypeptides and less then 27% identity to the green algal and vascular plant light-harvesting chlorophll polypeptides that bind both chlorophylls a and b, Its molecular mass as deduced from the gene sequence , is 18.4 kDa with three putative transmembrane helices and several residue s that may be involved in chlorophyll binding. The cDNA encoding the violax anthin-chlorophyll a polypeptide was used to isolate and characterize a 10 kb genomic fragment containing the entire gene. The open reading frame was interrupted by five introns ranging in size from 123 to 449 bp, The intron borders have typical eukaryotic GT ... AG sequences.