MOLECULAR-CLONING AND CHARACTERIZATION OF A DIHYDRODIPICOLINATE SYNTHASE (DHDPS) GENE FROM THE PHOTOAUTOTROPHIC PROKARYOTE PROCHLOROCOCCUS-MARINUS CCMP-1375 (PROCHLOROPHYTA)

The dapA gene coding for dihydrodipicolinate synthase (DHDPS; EC 4.2.1 .52) has been analyzed from the chlorophyll a and b containing photoau totrophic prokaryote Prochlorococcus marinus CCMP 1375. The dapA gene overlaps at its 5' end by 4 nucleotides with asd, coding for aspartate -semialdehyde dehydrogenase, another enzyme of the diaminopimelate pat hway of lysine biosynthesis. The deduced amino acid sequence of DHDPS has the highest degree of homology of known bacteria DHDPS to the corr esponding proteins in higher plants, with about 45 % identical or simi lar residues. In contrast to all other bacteria, an alanine is encoded at position 98 which corresponds to ala-112 in the mature maize DHDPS , known to be crucial for the allosteric plant-specific feedback inhib ition of DHDPS activity by lysine. Thus, evidence is provided for an e volutionary relatedness between plant and P. marinus DHDPS and for a p robably similar regulation of activity. These observations agree with the hypothesis that the plant gene originated from a transfer of a cya nobacterial-like endosymbiotic ancestor of chloroplasts to the nucleus .