DNA polymerase-alpha is the major replicative DNA polymerase in animal cells. The gene coding for a mutant DNA polymerase-alpha was transferred from one cell to another by transfection of DNA from mutant cells. The DNA was isolated from a mutant hamster cell line resistant to aphidicolin, a specific inhibitor of DNA polymerase-alpha, and transferred into an aphidicolin-sensitive cell line. The resulting transfectants exhibited increased survival in the presence of aphidicolin and contained an aphidicolin-resistant DNA polymerase-alpha.