Resolution of the diadenosine 5',5'''-P1,P4-tetraphosphate binding subunit from a multiprotein form of HeLa cell DNA polymerase α

A diadenosine 5',5'''-P1,P4-tetraphosphate (Ap4A) binding subunit has been resolved from a high molecular weight (640,000) multiprotein form of DNA polymerase α [deoxy-nucleoside triphosphate:DNA nucleotidyltransferase (DNA-directed), EC 2.7.7.7] from HeLa cells. The Ap4A binding activity copurifies with the DNA polymerizing activity during the course of purification. Hydrophobic chromatograpy on butylagarose resolves the Ap4A binding activity from the DNA polymerase. The Ap4A binding activity is protein in nature since the binding of Ap4A is abolished by treatment of the isolated binding activity with proteinase K but is insensitive to treatment with DNase or RNase. The molecular weight of the Ap4A binding protein, as determined by polyacrylamide gel electrophoresis under nondenaturing conditions or by NaDodSO4/polyacrylamide gel electrophoresis after photoaffinity labeling of the protein with [32P]Ap4A is 92,000 or 47,000. The binding activity of this protein is highly specific for Ap4A