Jarosz Daniel F, Godoy Veronica G, Delaney James C, Essigmann John M, Walker Graham C
Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Nature. 2006 Jan 12;439(7073):225-8. doi: 10.1038/nature04318.
Translesion synthesis (TLS) by Y-family DNA polymerases is a chief mechanism of DNA damage tolerance. Such TLS can be accurate or error-prone, as it is for bypass of a cyclobutane pyrimidine dimer by DNA polymerase eta (XP-V or Rad30) or bypass of a (6-4) TT photoproduct by DNA polymerase V (UmuD'2C), respectively. Although DinB is the only Y-family DNA polymerase conserved among all domains of life, the biological rationale for this striking conservation has remained enigmatic. Here we report that the Escherichia coli dinB gene is required for resistance to some DNA-damaging agents that form adducts at the N2-position of deoxyguanosine (dG). We show that DinB (DNA polymerase IV) catalyses accurate TLS over one such N2-dG adduct (N2-furfuryl-dG), and that DinB and its mammalian orthologue, DNA polymerase kappa, insert deoxycytidine (dC) opposite N2-furfuryl-dG with 10-15-fold greater catalytic proficiency than opposite undamaged dG. We also show that mutating a single amino acid, the 'steric gate' residue of DinB (Phe13 --> Val) and that of its archaeal homologue Dbh (Phe12 --> Ala), separates the abilities of these enzymes to perform TLS over N2-dG adducts from their abilities to replicate an undamaged template. We propose that DinB and its orthologues are specialized to catalyse relatively accurate TLS over some N2-dG adducts that are ubiquitous in nature, that lesion bypass occurs more efficiently than synthesis on undamaged DNA, and that this specificity may be achieved at least in part through a lesion-induced conformational change.
Y家族DNA聚合酶介导的跨损伤合成（TLS）是DNA损伤耐受的主要机制。这种TLS可能是准确的，也可能是易错的，例如DNA聚合酶η（XP-V或Rad30）绕过环丁烷嘧啶二聚体，以及DNA聚合酶V（UmuD'2C）绕过（6-4）TT光产物。尽管DinB是在生命的所有域中都保守的唯一Y家族DNA聚合酶，但这种显著保守性的生物学原理仍然是个谜。在这里，我们报告大肠杆菌dinB基因是对某些在脱氧鸟苷（dG）的N2位形成加合物的DNA损伤剂产生抗性所必需的。我们表明，DinB（DNA聚合酶IV）催化准确的TLS越过一种这样的N2-dG加合物（N2-糠基-dG），并且DinB及其哺乳动物同源物DNA聚合酶κ在N2-糠基-dG对面插入脱氧胞苷（dC）的催化效率比在未损伤的dG对面高10至15倍。我们还表明，将单个氨基酸（DinB的“空间门”残基Phe13突变为Val）及其古细菌同源物Dbh的（Phe12突变为Ala），会使这些酶在N2-dG加合物上进行TLS的能力与其复制未损伤模板的能力分离。我们提出，DinB及其同源物专门用于催化越过自然界中普遍存在的某些N2-dG加合物的相对准确的TLS，损伤绕过比在未损伤的DNA上合成更有效，并且这种特异性可能至少部分通过损伤诱导的构象变化来实现。
