Temporal and spatial distributions of yeast nucleoside diphosphate kinase activities and its association with the Cdc8p.

Abstract

Nucleoside diphosphate kinase (E.C. 2.7.4.6.) is a broad substrate-specific enzyme that catalyzes the phosphorylation of nucleoside diphosphates to the corresponding triphosphates in nucleic acid biosynthesis. In this report, we investigate its spatial and temporal distributions in yeast to understand how the enzyme exerts its gene function(s). Our results show that the enzyme is predominantly cytoplasmic. A substantial amount of enzyme activity (40-50%) may be associated with the cell membrane. Less than 1% of total activity was detected in the nuclear fraction. Approximately 3% was found in the mitochondrial fraction. When yeast cultures were synchronized, we found that Saccharomyces cerevisiae nucleoside diphosphate kinase did not show cell cycle periodicity, as Schizosaccharomyces pombe enzyme did. To explore its link with DNA synthesis, we investigated its relationship with the Cdc8p (dTMP kinase). We demonstrated a physical interaction between these proteins in vitro, as evidenced that the GST:Cdc8p protein affinity column could retain a subpopulation of nucleoside diphosphate kinase activity from yeast crude extract. Furthermore, when GST:Cdc8p protein was expressed in yeast, the protein could bind to the glutathione-agarose, along with nucleoside diphosphate kinase, suggesting that there is an interaction between GST:Cdc8p and nucleoside diphosphate kinase in vivo. Our results provide evidence for at least a two-enzyme complex that may well facilitate nucleotide channeling in the cell.