Friedberg E C, Minton K, Pawl G, Verzola P
J Virol. 1974 May;13(5):953-9. doi: 10.1128/JVI.13.5.953-959.1974.
Extracts of DNA polymerase I defective Escherichia coli infected with phage T4 contain an exonuclease activity that removes thymine dimers from UV-irradiated DNA previously nicked with T4 UV endonuclease. This activity is not expressed if cells are infected in the presence of chloramphenicol. The enzyme has a requirement for divalent cation and is not affected by caffeine, but excision is inhibited in the presence of proflavine. The enzyme is present in all phage T4 mutants thus far examined, including 25 UV-sensitive mutants isolated during the course of the experiments, all of which are defective in the v gene. A similar activity can be detected in cells infected with phages T2, T3, and T6, but not in cells infected with phage T7.
用噬菌体T4感染DNA聚合酶I缺陷型大肠杆菌后得到的提取物含有一种核酸外切酶活性，该活性可从先前用T4紫外线内切酶切割的紫外线照射过的DNA中去除胸腺嘧啶二聚体。如果在氯霉素存在的情况下感染细胞，则该活性不会表达。该酶需要二价阳离子，不受咖啡因影响，但在原黄素存在时切除作用受到抑制。到目前为止所检测的所有噬菌体T4突变体中都存在这种酶，包括在实验过程中分离出的25个紫外线敏感突变体，所有这些突变体的v基因都有缺陷。在用噬菌体T2、T3和T6感染的细胞中可检测到类似活性，但在用噬菌体T7感染的细胞中未检测到。
