CDNA CLONING AND CHARACTERIZATION OF THE NUCLEAR GENE ENCODING CHLOROPLAST GLYCERALDEHYDE-3-PHOSPHATE DEHYDROGENASE FROM THE MARINE RED ALGA GRACILARIA-VERRUCOSA

Using a PCR-generated homologous probe, we have recovered a cDNA (GapA cDNA) encoding the complete 338 amino-acid chloroplast GAPDH of the m arine red alga Gracilaria verrucosa, together with its 78 amino-acid t ransit peptide. This cDNA was readily aligned with chloroplast-localiz ed GAPDH genes (GapA and GapB) of green plants. The proline residue wh ich contributes to the specificity of NAD+ binding to cytosolic GAPDHs is absent from the deduced polypeptide chain of G. verrucosa GapA as is also the case in the chloroplast GAPDHs of plants. The transit pept ide shows a high proportion of random coil, an amino-terminal Met-Ala dipeptide, a high content of hydroxylamino acids, and a net positive c harge. The polyadenylation signal appears to be AGTAAA. Genomic Southe rn-hybridization data indicate that only one chloroplast-GAPDH gene ma y occur in G. verrucosa. Bootstrapped parsimony trees indicate that th e G. verrucosa GapA gene is a sister group to plant chloroplast-GAPDH genes, and are most readily interpreted as showing that red algal and plant chloroplast-localized GAPDHs arose in a single endosymbiotic eve nt.