When a high-fidelity DNA polymerase encounters certain DNA-damage sites, its progress can be stalled and one or more lesion-bypass polymerases are recruited to transit the lesion. Here, we consider two representative types of lesions: (i) 7,8-dihydro-8-oxogua-nine (8-oxoG), a small, highly prevalent lesion caused by oxidative damage; and (ii) bulky lesions derived from the environmental pre-carcinogen benzo [a]pyrene, in the high-fidelity DNA polymerase Bacillus fragment (BF) from Bacillus stearothermophilus and in the lesion-bypass DNA polymerase IV (Dpo4) from Sulfolobus solfataricus. The tight fit of the BF polymerase around the nascent base pair contrasts with the more spacious, solvent-exposed active site of Dpo4, and these differences in architecture result in distinctions in their respective functions: one-step versus stepwise polymerase translocation, mutagenic versus accurate bypass of 8-oxoG, and polymerase stalling versus mutagenic bypass at bulky benzo[a]pyrene-derived lesions.
Lesions and DNA polymerasesUntil 1999, it was widely understood that bacteria have three DNA polymerases and mammals have five [1]. In 1999, however, an entirely new category of polymerases was discovered in prokaryotes and eukaryotes [2-4] -the lesion-bypass DNA polymerases. The function of lesion-bypass polymerases is to replicate past lesion-containing DNA templates in a process called translesion synthesis [5][6][7]. Now at least 16 DNA polymerases are known in eukaryotes [8] and five in bacteria [9]. Furthermore, since 1999, crystal structures of DNA polymerases, including those containing lesions, have provided new structural insights into the mechanistic aspects of translesion synthesis and polymerase stalling associated with DNA lesions. For a review of the structures and mechanisms of DNA polymerases up to the year 2005, see Ref.[10].Here, we discuss the structural and functional features of representative high-fidelity and lesion-bypass DNA polymerases (Box 1) and how these features affect the processing of certain forms of DNA damage. The lesions considered are derived from reactions of intermediates produced by endogenous sources or from the metabolic activation of environmental genotoxic