Epigenetic modifications in bacteria, such as DNA methylation, have been shown to affect gene regulation, thereby generating cells that are isogenic but with distinctly different phenotypes. Restriction-modification (RM) systems contain prototypic methylases that are responsible for much of bacterial DNA methylation. This review focuses on a distinctive group of type I RM loci that , through phase variation, can modify their methylation target specificity and can thereby switch bacteria between alternative patterns of DNA methylation. Phase variation occurs at the level of the target recognition domains of the hsdS (specificity) gene via reversible recombination processes acting upon multiple hsdS alleles. We describe the global distribution of such loci throughout the prokaryotic kingdom and highlight the differences in loci structure across the various bacterial species. Although RM systems are often considered simply as an evolutionary response to bacteriophages, these multi-hsdS type I systems have also shown the capacity to change bacterial phenotypes. The ability of these RM systems to allow bacteria to reversibly switch between different physiological states, combined with the existence of such loci across many species of medical and industrial importance, highlights the potential of phase-variable DNA methylation to act as a global regulatory mechanism in bacteria.

中文翻译：

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I 型限制性修饰系统的相变甲基化和表观遗传调控。

细菌中的表观遗传修饰，如 DNA 甲基化，已被证明会影响基因调控，从而产生同基因但具有明显不同表型的细胞。限制性修饰 (RM) 系统包含负责大部分细菌 DNA 甲基化的原型甲基化酶。这篇综述着重于一组独特的 I 型 RM 基因座，这些基因座通过相位变异可以改变其甲基化靶标特异性，从而可以在 DNA 甲基化的替代模式之间切换细菌。通过作用于多个 hsdS 等位基因的可逆重组过程，相位变化发生在 hsdS（特异性）基因的目标识别域水平。我们描述了这些基因座在整个原核生物界的全球分布，并强调了不同细菌物种的基因座结构的差异。尽管 RM 系统通常被认为是对噬菌体的进化反应，但这些多 hsdS I 型系统也显示出改变细菌表型的能力。这些 RM 系统允许细菌在不同生理状态之间可逆地转换的能力，再加上在许多具有医学和工业重要性的物种中存在这样的基因座，突出了相位可变 DNA 甲基化作为一种​​全球调控机制的潜力。细菌。这些多 hsdS I 型系统也显示出改变细菌表型的能力。这些 RM 系统允许细菌在不同生理状态之间可逆地转换的能力，再加上在许多具有医学和工业重要性的物种中存在这样的基因座，突出了相位可变 DNA 甲基化作为一种​​全球调控机制的潜力。细菌。这些多 hsdS I 型系统也显示出改变细菌表型的能力。这些 RM 系统允许细菌在不同生理状态之间可逆地转换的能力，再加上在许多具有医学和工业重要性的物种中存在这样的基因座，突出了相位可变 DNA 甲基化作为一种​​全球调控机制的潜力。细菌。