cDNA cloning and characterization of the nuclear gene encoding chloroplast glyceraldehyde-3-phosphate dehydrogenase from the marine red alga Gracilaria verrucosa

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Abstract
Using a PCR-generated homologous probe, we have recovered a cDNA (GapA cDNA) encoding the complete 338 amino-acid chloroplast GAPDH of the marine red aga Gracilaria verrucosa, together with its 78 amino-acid transit peptide. This cDNA was readily aligned with chloroplast-localized GAPDH genes (GapA) and (GapB) of green plants. The proline residue which 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 peptide shows a high proportion of random coil, an amino-terminal Met-Ala dipeptide, a high content of hydroxylamino acids, and a net positive charge. The polyadenylation signal appears to the AGTAAA. Genomic Southernhybridization data indicate that only one chloroplast-GAPDH gene may occur in G. verrucosa. Bootstrapped parsimony trees indicate that the G. verrucosa Gap A 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 event.