Thymine and Uracil-thymine Dimers and Deoxyribonucleic Acid Synthesis in Mammalian Cells Irradiated with Ultraviolet Light

Summary

The ability of synchronized mammalian L cells to synthesize DNA during different time-intervals (between 1 and 24 hours) after different doses of u.v. light was studied. Thymine and uracil-thymine dimers formed in the DNA of irradiated cells do not completely block the DNA-synthesis. Cells irradiated with doses between 0 and 200 ergs shows a pronounced decrease in their ability to synthesize immediately after irradiation with DNA. But later on the amount of DNA synthesized by these cells gradually approaches the amount of DNA synthesized by non-irradiated cells. This process is dose-dependent.

Slow replication around the dimer block, resulting in production of mutated DNA together with the existence of many chromosomes with multiple origins of replication in a mammalian cell offer possible explanation of these findings.