Abstract
Ultraviolet light-induced DNA damage was found to inhibit SV40 origin-dependent DNA synthesis carried out by soluble human cell extracts. Replication of SV40-based plasmids was reduced to approx. 35% of that in unirradiated controls after irradiation with 50–100 J/m 2 germicidal ultraviolet light, where an average of 3–6 pyrimidine dimer photoproducts were formed per plasmid circle. Inhibition of the DNA helicase activity of T antigen (required for initiation of replication in the in vitro system) was also investigated, and was only significant after much higher fluences, 1000–5000 J/m 2. The data indicate that DNA damage by ultraviolet light inhibits DNA synthesis in cell-free extracts principally by affecting components of the replication complex other than the DNA helicase activity of T antigen. The soluble system could be used to biochemically investigate the possible bypass or tolerance of DNA damage during replication.
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