Identification and characterization of human deoxyguanosine kinase cDNA fragments

Mitochondria require deoxyribonucleoside triphosphates for the synthesis of their DNA and one of the enzymes responsible for the initial phosphorylation of purine deoxyribonucleoside is deoxyguanosine kinase (dGK; EC 2.7.1.113). Recent studies have suggested that dGK in addition to deoxycytidine kinase phosphorylates several anti-cancer agents, such as 9-β-d-arabinofuranosylguanine (Ara-G), cladribine (CdA), and fludarabine. There appear to coexist several mRNA fragments of dGK. In the present study we found 10 fragments, the longest fragment had 834 bp, and represented the entire open reading frame of dGK (780 bp). The nine additional fragments detected ranged from 807 to 269 bp. All the fragments were found to contain the specific mitochondria translocation signal sequence. Expression of these fragments in Escherichia coli demonstrated that only the full-length dGK resulted in a protein that could phosphorylate CdA and Ara-G. Given the difficulty to measure the full-length dGK, these data are of value for studying the mRNA gene expression of dGK in cell lines and in leukemic cells from patients.