DNA synthesis in normal and virus-transformed mammalian cells after methionine deprivation

Abstract

When mouse 3T3 cells or SV40-transformed 3T3 cells are deprived of methionine, nuclear DNA synthesis continues for several hours but is eventually inhibited. Newly-synthesized DNA becomes 30–40 % deficient in its normal complement of 5-methylcytosine, the only minor methylated base identified in the DNA from these cells. This suggests that some DNA synthesis occurs without DNA methylation but that methionine deprivation eventually results in the inhibition of DNA synthesis. There is some evidence that methyl-deficient DNA is stable in these cells. There were no significant differences between 3T3 and SV40-transformed 3T3 cells in the relationship between DNA synthesis and its methylation.