Human APOBEC3H and homologous single-stranded DNA cytosine deaminases are unique to mammals. These DNA-editing enzymes function in innate immunity by restricting the replication of viruses and transposons. APOBEC3H also contributes to cancer mutagenesis. Here, we address the fundamental nature of RNA in regulating human APOBEC3H activities. APOBEC3H co-purifies with RNA as an inactive protein, and RNase A treatment enables strong DNA deaminase activity. RNA-binding-defective mutants demonstrate clear separation of function by becoming DNA hypermutators. Biochemical and crystallographic data demonstrate a mechanism in which double-stranded RNA mediates enzyme dimerization. Additionally, APOBEC3H separation-of-function mutants show that RNA binding is required for cytoplasmic localization, packaging into HIV-1 particles, and antiviral activity. Overall, these results support a model in which structured RNA negatively regulates the potentially harmful DNA deamination activity of APOBEC3H while, at the same time, positively regulating its antiviral activity.

人类 APOBEC3H 和同源单链 DNA 胞嘧啶脱氨酶是哺乳动物独有的。这些 DNA 编辑酶通过限制病毒和转座子的复制在先天免疫中发挥作用。APOBEC3H 也有助于癌症诱变。在这里，我们讨论了 RNA 在调节人类 APOBEC3H 活动中的基本性质。APOBEC3H 与作为非活性蛋白的 RNA 共同纯化，而 RNase A 处理可实现强大的 DNA 脱氨酶活性。RNA 结合缺陷突变体通过成为 DNA 超突变体表现出明显的功能分离。生化和晶体学数据证明了双链 RNA 介导酶二聚化的机制。此外，APOBEC3H 功能分离突变体表明 RNA 结合是细胞质定位、包装成 HIV-1 颗粒和抗病毒活性所必需的。