Isolation and characterisation of components of the Dunaliella tertiolecta chloroplast genome

Three chloroplast genes, psbA, psbB and rbcL, of the microalgae Dunaliella tertiolecta were targeted with the view to using these components in the construction of a chloroplast transformation vector. The three genes and surrounding genomic regions were isolated by screening libraries and using degenerate primers to amplify by PCR conserved coding regions and unknown flanking sequences. The putative Dunaliella psbA, psbB and rbcL proteins show high levels of sequence conservation sharing approximately 87, 92 and 97% similarity to the homologues of Chlamydomonas reinhardtii. Interestingly, four of the five introns of the psbA gene contain long open-reading frames which have sequence similarity to the H-N-H and GIY-YIG site-specific homing endonucleases suggesting that, like other microalgae, the Dunaliella gene contains group I introns. Putative promoter regions of the psbB and rbcL genes were isolated and found to contain the required signals necessary for gene expression.