From the Department of Biochemistry and Molecular Biology, University of Texas Medical Branch at Galveston, Galveston, Texas 77555-1061.
J Biol Chem. 2014 May 9;289(19):13177-85. doi: 10.1074/jbc.M114.556977. Epub 2014 Mar 19.
The biological functions of human DNA polymerase (pol) θ, an A family polymerase, have remained poorly defined. Here we identify a role of polθ in translesion synthesis (TLS) in human cells. We show that TLS through the thymine glycol (TG) lesion, the most common oxidation product of thymine, occurs via two alternative pathways, in one of which, polymerases κ and ζ function together and mediate error-free TLS, whereas in the other, polθ functions in an error-prone manner. Human polθ is comprised of an N-terminal ATPase/helicase domain, a large central domain, and a C-terminal polymerase domain; however, we find that only the C-terminal polymerase domain is required for TLS opposite TG in human cells. In contrast to TLS mediated by polκ and polζ, in which polζ would elongate the chain from the TG:A base pair formed by polκ action, the ability of polθ alone to carry out the nucleotide insertion step, as well as the subsequent extension step that presents a considerable impediment due to displacement of the 5' template base, suggests that the polθ active site can accommodate highly distorting DNA lesions.
人类 DNA 聚合酶（pol）θ的生物学功能一直未被很好地定义，它是 A 家族聚合酶。在这里，我们确定了 polθ 在人类细胞中跨损伤合成（TLS）中的作用。我们表明，通过胸腺嘧啶二醇（TG）损伤的 TLS，即胸腺嘧啶最常见的氧化产物，通过两种替代途径发生，其中一种途径是聚合酶 κ 和 ζ 一起作用并介导无差错 TLS，而另一种途径中，polθ 以易错的方式发挥作用。人类 polθ 由 N 端 ATP 酶/解旋酶结构域、大的中央结构域和 C 端聚合酶结构域组成；然而，我们发现仅 C 端聚合酶结构域是人类细胞中针对 TG 进行 TLS 所必需的。与由 polκ 和 polζ 介导的 TLS 不同，在 polκ 作用形成的 TG:A 碱基对中，polζ 将延长链，而 polθ 单独进行核苷酸插入步骤的能力，以及由于 5'模板碱基的位移而带来的后续延伸步骤都存在相当大的障碍，表明 polθ 的活性位点可以容纳高度扭曲的 DNA 损伤。
