DNA methylation is ubiquitously found in all three domains of life. This epigenetic modification on adenine or cytosine residues serves to regulate gene expression or to defend against invading DNA in bacteria. Here, we report the significance of N6-methyladenine (6mA) to epigenetic immunity in Deinococcus radiodurans. Putative protein encoded by DR_2267 ORF (Dam2_DR) contributed 35% of genomic 6mA in D. radiodurans but did not influence gene expression or radiation resistance. Dam2_DR was characterized to be a functional S-adenosyl methionine (SAM)-dependent N6-adenine DNA methyltransferase (MTase) but with no endonuclease activity. Adenine methylation from Dam2_DR or Dam1_DR (N6-adenine MTase encoded by DR_0643) improved DNA uptake during natural transformation. To the contrary, methylation from Escherichia coli N6-adenine MTase (Dam_EC that methylates adenine in GATC sequence) on donor plasmid drastically reduced DNA uptake in D. radiodurans, even in presence of Dam2_DR or Dam1_DR methylated adenines. With these results, we conclude that self-type N6-adenine methylation on donor DNA had a protective effect in absence of additional foreign methylation, a separate methylation-dependent Restriction Modification (R-M) system effectively identifies and limits uptake of G6mATC sequence containing donor DNA. This is the first report demonstrating presence of epigenetic immunity in D. radiodurans.

DNA甲基化在生命的所有三个领域中无处不在。这种对腺嘌呤或胞嘧啶残基的表观遗传修饰用于调节基因表达或抵御细菌中的 DNA 入侵。在这里，我们报告了 N6-甲基腺嘌呤 (6mA) 对耐辐射奇异球菌的表观遗传免疫的重要性。由 DR_2267 ORF (Dam2 _DR )编码的推定蛋白质在D. radiodurans 中贡献了基因组 6mA 的 35%，但不影响基因表达或辐射抗性。Dam2 _DR被表征为功能性 S-腺苷甲硫氨酸 (SAM) 依赖性 N6-腺嘌呤 DNA 甲基转移酶 (MTase)，但没有核酸内切酶活性。从Dam2腺嘌呤甲基化_DR或Dam1 _DR（由 DR_0643 编码的 N6-腺嘌呤 MTase）提高了自然转化过程中的 DNA 吸收。相反，甲基化从大肠杆菌N6 -腺嘌呤转移酶（坝_EC，在GATC序列甲醇盐腺嘌呤）上的供体质粒急剧降低的DNA摄取在耐辐射球菌，即使在Dam2的存在_DR或Dam1 _DR甲基化腺嘌呤。根据这些结果，我们得出结论，供体 DNA 上的自身型 N6-腺嘌呤甲基化在没有额外外源甲基化的情况下具有保护作用，单独的甲基化依赖性限制修饰 (RM) 系统有效地识别并限制了含有供体 DNA 的 G6mATC 序列的摄取. 这是第一份证明表观遗传免疫存在于D. 耐辐射。