recN E.coli mutant大肠杆菌DNA修复系统基因缺失突变菌株-BioVector NTCC保藏中心

recN E.coli mutant大肠杆菌基因缺失菌株-BioVector NTCC保藏中心

Gene Symbol突变基因名称：recN
Mnemonic:recombination
Synonyms别称：radB
Gene product基因产物：LexA regulon; recombination and repair
Selectable Phenotype筛选表型：sensitive to mitomycin C  (2 μg/ml) and gamma radiation
Culture Condition培养条件：Luria broth
Other Phenotypes其他表型：
Notes：
Reference参考文献：Picksley, S. M. et al.
Mol. Gen. Genet. 1984. 195: 267-274

RecN E. coli mutant strain is a genetically modified bacterium that has a non-functional or deleted RecN gene. The RecN protein is a crucial component of the DNA repair system in E. coli, specifically involved in fixing double-strand breaks (DSBs).

Here's a breakdown of what that means for the mutant strain and its phenotype (observable characteristics):

The Function of RecN Protein

In wild-type (normal) E. coli, the RecN protein is a member of the SMC (Structural Maintenance of Chromosomes) family of proteins. Its primary roles in DNA repair include:

• Responding to DNA damage: The recN gene is part of the SOS response, a global cellular reaction to DNA damage. When the cell's DNA is severely harmed, the expression of RecN is significantly increased.

• DNA repair complex formation: RecN helps organize and stabilize DNA repair complexes, acting like a scaffold or clamp that holds broken DNA ends together. It's often found colocalizing with RecA, another key protein in DNA recombination and repair.

• Maintaining chromosome structure: RecN is critical for maintaining sister chromatid cohesion during the repair process, which ensures that the homologous chromosome is available as a template for accurate repair.

Phenotype of a RecN Mutant

When the recN gene is mutated or deleted (often designated as ΔrecN), the E. coli strain loses the ability to properly perform these functions. This results in several observable phenotypes:

• Sensitivity to DNA-damaging agents: The most prominent characteristic is a hypersensitivity to DNA-damaging agents that cause double-strand breaks. These include:

  • Mitomycin C (MMC): A DNA-crosslinking agent.

  • Ionizing radiation (gamma rays): Causes direct breaks in the DNA backbone.

• Reduced recombination efficiency: RecN mutants are deficient in homologous recombination, which is the primary pathway for repairing double-strand breaks in E. coli. This can be measured by a decreased ability to repair I-SceI-induced double-strand breaks and reduced transductional recombination.

• No UV sensitivity: Interestingly, unlike mutants in other key repair genes like uvrA or recJ, a recN single mutant is generally not sensitive to UV radiation. This suggests that RecN's role is highly specific to double-strand breaks and not the single-strand gaps or pyrimidine dimers typically caused by UV light.

• Defective nucleoid reorganization: In the face of severe DNA damage, E. coli undergoes a process of DNA supercompaction or nucleoid reorganization. RecN has been shown to be essential for this process, so the mutant strain fails to properly compact its nucleoid after DNA damage.

RecN 大肠杆菌突变株 是一种基因被修改的大肠杆菌，其 RecN 基因功能缺失或被删除。RecN 蛋白是大肠杆菌 DNA 修复系统的关键组成部分，尤其在修复 **DNA 双链断裂（DSBs）**方面发挥着重要作用。

以下是关于这种突变株及其表型（可观察到的特性）的详细说明：

RecN 蛋白的功能

在野生型（正常）大肠杆菌中，RecN 蛋白 属于 SMC（染色体结构维持）蛋白家族。它在 DNA 修复中的主要作用包括：

• 响应 DNA 损伤：recN 基因是 SOS 响应的一部分，SOS 响应是一种细胞在面对 DNA 严重损伤时所产生的全局反应。当细胞的 DNA 受到严重损伤时，RecN 的表达量会显著增加。

• 形成 DNA 修复复合物： RecN 蛋白就像一个支架或夹子，帮助组织和稳定 DNA 修复复合物，将断裂的 DNA 末端固定在一起。它通常与 RecA（另一种 DNA 重组和修复的关键蛋白）共同定位。

• 维持染色体结构： 在修复过程中，RecN 对于维持姐妹染色单体粘连至关重要，这能确保同源染色体可作为精确修复的模板。

RecN 突变株的表型

当 recN 基因发生突变或被删除时（通常标记为 ΔrecN），大肠杆菌菌株将无法正常执行上述功能。这导致了几个明显的表型特征：

• 对 DNA 损伤剂的敏感性： 最显著的特征是它对能引起双链断裂的 DNA 损伤剂极度敏感。这些损伤剂包括：

  • 丝裂霉素 C (Mitomycin C, MMC)： 一种 DNA 链间交联剂。

  • 电离辐射（伽马射线）： 直接造成 DNA 主链断裂。

• 重组效率降低： RecN 突变株在同源重组方面存在缺陷，而同源重组是大肠杆菌修复双链断裂的主要途径。这可以通过其修复由 I-SceI 酶引起的双链断裂的能力减弱来衡量。

• 对紫外线不敏感： 有趣的是，与 uvrA 或 recJ 等其他关键修复基因的突变株不同，recN 单一突变株通常对紫外线辐射不敏感。这表明 RecN 的作用高度特异于双链断裂，而非由紫外线通常引起的单链缺口或嘧啶二聚体。

• 核样体重组缺陷： 在面临严重的 DNA 损伤时，大肠杆菌会经历 DNA 超级压缩或核样体重组。研究表明 RecN 对此过程至关重要，因此突变株在 DNA 损伤后无法正确压缩其核样体。

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