RecA is essential for Double-Strand Break Repair (DSBR) and the SOS response in Escherichia coli K-12. RecN is an SOS protein and member of the Structural Maintenance of Chromosomes (SMC) family of proteins thought to play a role in sister chromatid cohesion/interactions during DSBR. Previous studies have shown that a plasmid-encoded recA4190 (Q300R) mutant had a phenotype similar to ΔrecN (mitomycin C sensitive and UV resistant). It was hypothesized that RecN and RecA physically interact and that recA4190 specifically eliminated this interaction. To test this model, an epistasis analysis between recA4190 and ΔrecN was performed in wild-type and recBC sbcBC cells. To do this, recA4190 was first transferred to the chromosome. As single mutants, recA4190 and ∆recN were Rec⁺ as measured by transductional recombination, but were 3-fold and 10-fold decreased in their ability to do I-SceI-induced DSBR, respectively. In both cases, the double mutant had an additive phenotype relative to either single mutant. In the recBC sbcBC background, recA4190 and ∆recN cells were very UV^S, Rec^- , had high basal levels of SOS expression and an altered distribution of RecA-GFP structures. In all cases, the double mutant had additive phenotypes. These data suggest that recA4190 (Q300R) and ∆recN remove functions in genetically distinct pathways important for DNA repair and that RecA Q300 was not important for an interaction between RecN and RecA in vivorecA4190 (Q300R) revealed modest phenotypes in a wild-type background and dramatic phenotypes in a recBC sbcBC strain reflecting greater stringency of RecA's role in that background.

中文翻译：

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大肠杆菌 K-12 中的recA和recN的上位性分析。


RecA 对于大肠杆菌K-12 中的双链断裂修复 (DSBR) 和 SOS 反应至关重要。 RecN 是一种 SOS 蛋白，也是染色体结构维持 (SMC) 蛋白家族的成员，被认为在 DSBR 期间的姐妹染色单体凝聚/相互作用中发挥作用。先前的研究表明，质粒编码的recA4190 （Q300R）突变体具有与ΔrecN （丝裂霉素C敏感且抗紫外线）相似的表型。假设 RecN 和 RecA 在物理上相互作用，而recA4190专门消除了这种相互作用。为了测试该模型，在野生型和recBC sbcBC细胞中进行了recA4190和ΔrecN之间的上位分析。为此， recA4190首先被转移到染色体上。作为单一突变体， recA4190和ΔrecN通过转导重组测量为 Rec ⁺ ，但 I- Sce I 诱导 DSBR 的能力分别下降了 3 倍和 10 倍。在这两种情况下，双突变体相对于任一单突变体都具有加性表型。在recBC sbcBC背景中， recA4190和ΔrecN细胞的UV ^S 、Rec ^-非常强，具有高基础水平的SOS表达和RecA-GFP结构的分布改变。在所有情况下，双突变体都具有加性表型。 这些数据表明， recA4190 （Q300R）和ΔrecN消除了对DNA修复重要的遗传上不同的途径中的功能，并且RecA Q300对于体内RecN和RecA之间的相互作用并不重要recA4190 （Q300R）在野生型背景中揭示了适度的表型以及recBC sbcBC菌株中引人注目的表型，反映出RecA在该背景下的作用更加严格。