DNA is exposed to the attack of several exogenous agents that modify its chemical structure, so cells must repair those changes in order to survive. Alkylating agents introduce methyl or ethyl groups in most of the cyclic or exocyclic nitrogen atoms of the ring and exocyclic oxygen available in DNA bases producing damage that can induce the SOS response in Escherichia coli and many other bacteria. Likewise, ultraviolet light produces mainly cyclobutane pyrimidine dimers that arrest the progression of the replication fork and triggers such response. The need of some enzymes (such as RecO, ExoI and RecJ) in processing injuries produced by gamma radiation prior the induction of the SOS response has been reported before. In the present work, several repair-defective strains of E. coli were treated with methyl methanesulfonate, ethyl methanesulfonate, mitomycin C or ultraviolet light. Both survival and SOS induction (by means of the Chromotest) were tested. Our results indicate that the participation of these genes depends on the type of injury caused by a genotoxin on DNA.

DNA 会受到多种外源性物质的攻击，这些物质会改变其化学结构，因此细胞必须修复这些变化才能生存。烷化剂在环的大多数环状或环外氮原子中引入甲基或乙基，并在 DNA 碱基中可用的环外氧产生损伤，从而在大肠杆菌和许多其他细菌中诱导 SOS 反应。同样，紫外线主要产生环丁烷嘧啶二聚体，其阻止复制叉的进程并触发这种反应。之前已经报道了在诱导 SOS 反应之前需要一些酶（例如 RecO、ExoI 和 RecJ）来处理由伽马辐射产生的损伤。在目前的工作中，大肠杆菌的几种修复缺陷菌株用甲磺酸甲酯、甲磺酸乙酯、丝裂霉素C或紫外光处理。测试了存活率和 SOS 诱导（通过 Chromotest）。我们的结果表明，这些基因的参与取决于基因毒素对 DNA 造成的损伤类型。