Isolation of an intact DNA polymerase-primase from embryos of Drosophila melanogaster.

A procedure has been devised for the purification of intact DNA polymerase alpha from early embryos of Drosophila melanogaster. The purified enzyme consists of at least three polypeptides with Mrs of 182,000, 60,000, and 50,000. These are related antigenically to the alpha (Mr 148,000), beta (Mr 58,000), and gamma (Mr 46,000) subunits, respectively, of the DNA polymerase described previously [Banks, G. R., Boezi, J. A. & Lehman, I. R. (1979) J. Biol. Chem. 254, 9886-9892]. The alpha subunit (Mr 182,000) has a molecular weight indistinguishable from that observed in extracts of freshly harvested embryos and presumably present in vivo. As in the previous preparation, the alpha subunit is required for DNA polymerase activity and is very likely the catalytic subunit of the enzyme. The ratio of primase to polymerase remains constant throughout the purification. Thus, the primase is very likely an integral component of the Drosophila DNA polymerase alpha. The purified DNA polymerase-primase contains no detectable endo- or exodeoxyribonuclease and has pH, MgCl2, (NH4)2SO4, and NaCl optima identical to those reported previously. In contrast, the Km for dTTP is 3.7 microM as compared with 17.5 microM for the previous enzyme. Sensitivities to aphidicolin and N-ethylmaleiimide and resistance to dideoxy TTP are unchanged.