人 APOBEC 单链 (ss) 特异性 DNA 和 RNA 胞苷脱氨酶可将胞嘧啶转变为尿嘧啶，并在抗病毒先天免疫、RNA 编辑中发挥作用，并可引起染色体超突变。产生的尿嘧啶可以直接复制，导致 C 到 T 突变，或者尿嘧啶-DNA 糖基化酶可以将尿嘧啶转化为脱碱基 (AP) 位点，然后通过跨损伤 DNA 聚合酶将其固定为 C 到 T 或 C 到 G 突变。我们注意到，在酵母和人类癌症中，C 到 T 和 C 到 G 突变的贡献取决于 APOBEC 诱变的 ssDNA 的起源。由于真核基因组中的 ssDNA 很容易与复制蛋白 A (RPA) 结合，我们询问 RPA 是否会影响酵母中 APOBEC 诱导的突变谱。为此，我们在野生型酵母和大 RPA 亚基中携带亚型突变 rfa1-t33 的菌株中表达人类 APOBEC。我们证实 rfa1-t33 等位基因可以促进 APOBEC 的诱变。我们还发现，rfa1-t33 突变改变了复制酵母中 APOBEC3A 诱导的 T 与 C 和 T 与 G 突变的比率，类似于在酵母和癌症中长期持续的 ssDNA 中观察到的比率。我们提供的数据表明，RPA 可以保护 ssDNA 中 APOBEC 形成的尿嘧啶免受 Ung1 的影响，从而通过复制 DNA 聚合酶准确复制尿嘧啶，促进 C 到 T 诱变。出乎意料的是，我们还发现，对于通过野生型 RPA 屏蔽 Ung1 的尿嘧啶，在存在跨损伤 DNA 聚合酶 zeta 的情况下，诱变结果会减少。由牛津大学出版社代表美国遗传学会出版，2024 年。

Human APOBEC single-strand (ss) specific DNA and RNA cytidine deaminases change cytosines to uracils and function in antiviral innate immunity, RNA editing, and can cause hypermutation in chromosomes. The resulting uracils can be directly replicated, resulting in C to T mutations, or uracil-DNA glycosylase can convert the uracils to abasic (AP) sites which are then fixed as C to T or C to G mutations by translesion DNA polymerases. We noticed that in yeast and in human cancers, contributions of C to T and C to G mutations depends on the origin of ssDNA mutagenized by APOBECs. Since ssDNA in eukaryotic genomes readily binds to replication protein A (RPA) we asked if RPA could affect APOBEC-induced mutation spectrum in yeast. For that purpose, we expressed human APOBECs in the wild-type yeast and in strains carrying a hypomorph mutation rfa1-t33 in the large RPA subunit. We confirmed that the rfa1-t33 allele can facilitate mutagenesis by APOBECs. We also found that the rfa1-t33 mutation changed the ratio of APOBEC3A-induced T to C and T to G mutations in replicating yeast to resemble a ratio observed in long-persistent ssDNA in yeast and in cancers. We present the data suggesting that RPA may shield APOBEC formed uracils in ssDNA from Ung1, thereby facilitating C to T mutagenesis through the accurate copying of uracils by replicative DNA polymerases. Unexpectedly, we also found that for uracils shielded from Ung1 by wild-type RPA the mutagenic outcome is reduced in the presence of translesion DNA polymerase zeta.Published by Oxford University Press on behalf of The Genetics Society of America 2024.