SEPARATE NUCLEAR GENES ENCODE CYTOSOLIC AND MITOCHONDRIAL NUCLEOSIDE DIPHOSPHATE KINASE IN DICTYOSTELIUM-DISCOIDEUM

We have previously isolated cDNA clones for the gip17 gene encoding th e cytosolic nucleoside diphosphate (NDP) kinase from Dictyostelium dis coideum, and partial cDNAs for guk, a second member of the NDP kinase gene family (Wallet, V., Mutzel, R., Troll, H., Barzu, O., Wurster, B. , Veron, M., and Lacombe, M. L. (1990) J. Natl. Cancer Inst. 80, 1199- 1202). We now characterize genomic DNA clones for both NDP kinase gene s, and we show that guk defines a nuclear-encoded mitochondrial NDP ki nase. Isolated D. discoideum mitochondria contain 3% of the total cell ular NDP kinase activity. Antibodies which specifically recognize and inhibit the activity of either cytosolic or mitochondrial NDP kinase u nambiguously distinguish between these activities. The nascent mitocho ndrial NDP kinase contains a presequence of 57 amino acids that is rem oved during import into the organelle as shown by determination of the NH2 terminus of the mature protein from mitochondria. The genes for m itochondrial and cytosolic NDP kinases contain four and two introns, r espectively. The positions of the introns in the gene for the cytosoli c enzyme match exactly the positions of the second and fourth introns in the coding region of its mitochondrial homologue. From these result s we conclude that the isozymes diverged from a common ancestor, and w e discuss possible phylogenetic pathways for the evolution of cytosoli c and organelle NDP kinases.