Decreased de novo DNA-Thymine Synthesis and Increased Thymidine- 3 H Incorporation into DNA by Human Bone Marrow Cultured with Aminopterin. ∗

Summary

When incubated with normal human bone marrow cells in the presence of 624 L-serine-3-¹⁴C and thymidine-³H, aminopterin decreases de novo synthesis of DNA-thymine-¹⁴C to 16%, while incorporation of thymidine-³H into DNA is increased to 140% of control values. These results are interpreted as evidence for increased utilization of preformed thymidine in DNA synthesis in the presence of aminopterin. The possible mechanisms for this increased incorporation of preformed thymidine into DNA in the presence of aminopterin are discussed.