Diadenosine 5',5'''-P1,P4-tetraphosphate, a ligand of the 57-kilodalton subunit of DNA polymerase alpha.

By equilibrium dialysis a disadenosine 5',5'''-P1,P2-tetraphosphate (Ap4A) binding activity is shown to be present in mammalian cells. The Ap4A binding activity copurifies with DNA polymerase alpha during the isolation procedure, which includes chromatography on phospho-, DEAE-, and DNA-cellulose; gel filtration; sucrose gradient centrifugation; and electrophoresis in nondenaturing polyacrylamide gels. After these purification steps, DNA polymerase alpha appears to be homogeneous in nondenaturing polyacrylamide gels.