Polynucleotide Kinase-3-Phosphatase (PNKP)

PNKP contains a putative ATP-binding site and a potential 3-prime phosphatase domain with similarity to L-2 haloacid dehalogenases. Database searches identified possible homologs in C. elegans, S. pombe, and Drosophila. A second signal of about 7.5 kb was also observed, with highest intensity in spleen. A glutathione S-transferase-PNKP fusion protein displayed 5-prime DNA kinase and 3-prime phosphatase activities. The authors stated that PNKP was the first gene identified for a DNA-specific kinase from any organism. PNKP expression partially rescued the sensitivity to oxidative damaging agents of the E. coli DNA repair-deficient 'xth nfo' double mutant. Furthermore, PNKP gene function restored termini suitable for DNA polymerase, consistent with in vivo removal of 3-prime phosphate groups, facilitating DNA repair.