Strikingly different properties of uracil-DNA glycosylases UNG2 and SMUG1 may explain divergent roles in processing of genomic uracil
Strikingly different properties of uracil-DNA glycosylases UNG2 and SMUG1 may explain divergent roles in processing of genomic uracil
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DOI：
10.1016/j.dnarep.2012.03.003
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发表时间：
2012-06-01
期刊：
影响因子：
3.8
通讯作者：
Kavli, Bodil
中科院分区：
文献类型：
--
作者：
Doseth, Berit;Ekre, Cecilie;Kavli, Bodil
由自发脱氨基胞嘧啶产生的基因组尿嘧啶会产生诱变的 U:G 错配，通常可以通过无错碱基切除修复 (BER) 来纠正。然而，在 B 细胞中，激活诱导的胞嘧啶脱氨酶 (AID) 会在 Ig 基因座的热点序列中产生 U:G 错配。这些在体细胞超突变 (SHM) 和类别转换重组 (CSR) 过程中会受到诱变处理。尿嘧啶 N-糖基化酶 UNG2 和 SMUG1（单链选择性单功能尿嘧啶 DNA 糖基化酶 I）在大多数 DNA 环境中启动无错 BER，但 UNG2 也参与了抗体多样化过程中 AID 诱导的尿嘧啶的诱变过程，其调节机制尚不清楚。 AID 是严格单链特异性的。在这里，我们表明，在 Mg2+ 和单价盐存在的情况下，人和小鼠 SMUG1 本质上是双链特异性的，而 UNG2 在所有测试条件下都能有效去除单链和双链 DNA 中的尿嘧啶。此外，SMUG1 和 UNG2 显示出截然不同的序列偏好。有趣的是，UNG2 从单链 DNA 中去除 AID 热点序列中尿嘧啶的效率是 SMUG1 的 200 倍。这或许可以解释为什么未排除在Ig位点之外的SMUG1无法在抗体多样化中替代UNG2。我们提出了一种诱变处理模型，其中复制蛋白 A (RPA) 将 UNG2 招募到脱氨基位点并使 DNA 保持单链构象，从而避免脱氨基胞嘧啶的无错误 HER。 (C) 2012 Elsevier B.V. 保留所有权利。
Genomic uracil resulting from spontaneously deaminated cytosine generates mutagenic U:G mismatches that are usually corrected by error-free base excision repair (BER). However, in B-cells, activation-induced cytosine deaminase (AID) generates U:G mismatches in hot-spot sequences at Ig loci. These are subject to mutagenic processing during somatic hypermutation (SHM) and class switch recombination (CSR). Uracil N-glycosylases UNG2 and SMUG1 (single strand-selective monofunctional uracil-DNA glycosylase I) initiate error-free BER in most DNA contexts, but UNG2 is also involved in mutagenic processing of AID-induced uracil during the antibody diversification process, the regulation of which is not understood. AID is strictly single strand-specific. Here we show that in the presence of Mg2+ and monovalent salts, human and mouse SMUG1 are essentially double strand-specific, whereas UNG2 efficiently removes uracil from both single and double stranded DNA under all tested conditions. Furthermore, SMUG1 and UNG2 display widely different sequence preferences. Interestingly, uracil in a hot-spot sequence for AID is 200-fold more efficiently removed from single stranded DNA by UNG2 than by SMUG1. This may explain why SMUG1 which is not excluded from Ig loci, is unable to replace UNG2 in antibody diversification. We suggest a model for mutagenic processing in which replication protein A (RPA) recruits UNG2 to sites of deamination and keeps DNA in a single stranded conformation, thus avoiding error-free HER of the deaminated cytosine. (C) 2012 Elsevier B.V. All rights reserved.