Cassuto E, Mursalim J, Howard-Flanders P
Proc Natl Acad Sci U S A. 1978 Feb;75(2):620-4. doi: 10.1073/pnas.75.2.620.
An in vitro system is described in which the cutting of crosslinked phiX replicative form (RF) I DNA molecules by the uvr system of Escherichia coli induces the cutting of homologous undamaged DNA during incubation with crude extracts of thermally induced E. coli (lambda precA+) lysogens. This reaction, which has also been observed in intact E. coli lysogens infected with lambda phages, is dependent on the presence of functional recA+ and uvrB+ gene products. Extracts from thermally induced lambda precA+ lysogens of E. coli proved to be substantially more active than extracts from nonlysogenic cells of the same strain. The results provide preliminary evidence for an endonuclease activity that cuts intact superhelical DNA in response to interaction with homologus damaged DNA. In the present paper, we describe an in vitro system in which both the endonucleolytic cutting of DNA containing crosslinks and the induced cutting of undamaged DNA can be studied without purification of the participating enzymes. Although the information obtained is fragmentary and often puzzling, we feel that this system can contribute to an understanding of the complex mechanisms involved in repair and recombination.
本文描述了一种体外系统，在该系统中，大肠杆菌uvr系统切割交联的φX复制型（RF）I DNA分子，会在与热诱导的大肠杆菌（λprecA+）溶原菌的粗提物孵育期间，诱导切割同源的未受损DNA。这种反应，在感染了λ噬菌体的完整大肠杆菌溶原菌中也观察到，它依赖于功能性recA+和uvrB+基因产物的存在。事实证明，来自热诱导的大肠杆菌λprecA+溶原菌的提取物比来自同一菌株非溶原性细胞的提取物活性要高得多。这些结果为一种核酸内切酶活性提供了初步证据，该活性会响应与同源受损DNA的相互作用而切割完整的超螺旋DNA。在本文中，我们描述了一种体外系统，在该系统中，可以在不纯化参与的酶的情况下，研究含有交联的DNA的内切核酸酶切割以及未受损DNA的诱导切割。尽管所获得的信息是零碎的，而且常常令人困惑，但我们认为这个系统有助于理解参与修复和重组的复杂机制。
