1. Henderson, J. F., and Paterson, A. R. P. (eds.) (1973).Nucleotide Metabolism: An Introduction. Academic Press, New York.
2. Littlefield, J. W. (1976).Variation, Senescence and Neoplasia in Cultured Somatic Cells. Harvard University Press, Cambridge.
3. De Mars, R. (1974).Mutation Res. 24:335?364.
4. Lieberman, I., and Ove, P. (1960).J. Biol. Chem. 235:1765?1768.
5. Atkin, J. H., and Gartler, S. M. (1968).Genetics 60:781?792.