Characterization and purification of a novel dATP-binding protein in eukaryotes

We characterized and purified an acidic dATP-binding protein, which, in its active form, resides in the nuclear fraction of a range of cells from mammals (including pig liver) and baker's yeast (Saccharomyces cerevisiae). This protein exhibits a high degree of specificity for the deoxy form of the naturally occurring nucleoside triphosphates and shows a marked preference for the purine deoxynucleoside triphosphates dATP and dGTP. The protein cleaves the terminal phosphate of dATP and appears to retain the dADP moiety of the nucleotide in a reaction that is resistant to both SDS and 8 M-urea. Fractionation of the nuclear preparation followed by non-denaturing PAGE and SDS/PAGE electrophoresis was sufficient to produce pure protein. The occurrence of this activity in all nuclei tested suggests that it plays an important role in nuclear metabolism. The specificity of the enzyme for deoxynucleoside triphosphates further suggests a role for this enzyme in DNA replication or repair, but the acidity of the protein argues against a direct interaction with DNA, and, indeed, the catalytic activity is not modulated by the inclusion of DNA in a variety of physical forms.