Cell-cycle regulation, intracellular sorting and induced overexpression ofthe human NTH1 DNA glycosylase involved in removal of formamidopyrimidine residues from DNA

Endonuclease III (Nth) of Escherichia coli is a DNA glycosylase essential f or the removal of oxidised pyrimidine base residues from DNA. Several eukar yotic homologues have recently been identified and shown to have biochemica l properties similar to those of Nth. However, some of the eukaryotic count erparts also appear to remove imidazole ring-opened purine residues (faPy), a property not shared by the enzymes of bacterial origin. Here, we show th at the human enzyme also possesses efficient faPy DNA glycosylase activity as indicated both from studies of the purified protein and induced overexpr ession of the human NTH1 cDNA in HeLa cells. We constructed green fluoresce nt protein-tagged hNTH1 fusion proteins to study the cellular localisation of hNTH1 and found strong and exclusive sorting to the nucleus. Studies wit h synchronised cells showed that the expression of hNTH1 is regulated durin g the cell cycle with increased transcription during early and mid S-phase. (C) 2000 Elsevier Science B.V. All rights reserved.