McDonald John P, Frank Ekaterina G, Plosky Brian S, Rogozin Igor B, Masutani Chikahide, Hanaoka Fumio, Woodgate Roger, Gearhart Patricia J
Laboratory of Genomic Integrity, Building 6, Room 1A13, NICHD, NIH, 9000 Rockville Pike, Bethesda, MD 20892-2725, USA.
J Exp Med. 2003 Aug 18;198(4):635-43. doi: 10.1084/jem.20030767.
Recent studies suggest that DNA polymerase eta (poleta) and DNA polymerase iota (poliota) are involved in somatic hypermutation of immunoglobulin variable genes. To test the role of poliota in generating mutations in an animal model, we first characterized the biochemical properties of murine poliota. Like its human counterpart, murine poliota is extremely error-prone when catalyzing synthesis on a variety of DNA templates in vitro. Interestingly, when filling in a 1 base-pair gap, DNA synthesis and subsequent strand displacement was greatest in the presence of both pols iota and eta. Genomic sequence analysis of Poli led to the serendipitous discovery that 129-derived strains of mice have a nonsense codon mutation in exon 2 that abrogates production of poliota. Analysis of hypermutation in variable genes from 129/SvJ (Poli-/-) and C57BL/6J (Poli+/+) mice revealed that the overall frequency and spectrum of mutation were normal in poliota-deficient mice. Thus, either poliota does not participate in hypermutation, or its role is nonessential and can be readily assumed by another low-fidelity polymerase.
近期研究表明，DNA聚合酶η（polη）和DNA聚合酶ι（polι）参与免疫球蛋白可变基因的体细胞超突变。为了在动物模型中测试polι在产生突变中的作用，我们首先对小鼠polι的生化特性进行了表征。与人类的polι类似，小鼠polι在体外催化多种DNA模板的合成时极易出错。有趣的是，在填补1个碱基对的缺口时，同时存在polι和polη时DNA合成及随后的链置换最为显著。对Polι的基因组序列分析意外发现，129品系的小鼠在第2外显子中有一个无义密码子突变，该突变消除了polι的产生。对129/SvJ（Polι-/-）和C57BL/6J（Polι+/+）小鼠可变基因中的超突变分析表明，在缺乏polι的小鼠中，突变的总体频率和谱是正常的。因此，要么polι不参与超突变，要么其作用并非必不可少，可轻易被另一种低保真度聚合酶替代。
