The effect of oxidized guanines on DNA synthesis by DNA polymerase β

Abstract

DNA replication is the fundamental biological task of duplicating genetic information for passing on to a daughter cell. DNA polymerases are the molecular machines that read the parent DNA strand and instruct the addition of correct corresponding nucleotides (also termed fidelity) to form a new DNA strand. DNA replication is extremely accurate to prevent deleterious alterations to the genetic code. However, DNA is damaged more than 10,000 times per cell per day. 8-oxo-7,8-dihydro-2ʹ-guanosine (8-oxo-G) is a form of DNA oxidative damage that threatens fidelity by base pairing with both a canonical cytosine and a non-canonical adenine. Due to its dual coding potential, DNA polymerases frequently make the mistake of inserting adenine instead of cytosine during DNA replication. We hypothesized that other oxidized guanines, such as 4,6-diamino-5-formamidopyrimidine (Fapy•dG) and 7,8-dihydro-8-oxo-riboguanosine (r8-oxo-G), may also be error-prone during DNA polymerase processing. To evaluate the mutagenicity of Fapy•dG and r8-oxo-G, we employed a well-characterized human DNA polymerase involved in DNA repair, DNA polymerase β (pol β). This work broadly shows that pol β has similar strategies for excluding damaged nucleotide triphosphates, but unique mechanistic barriers in response to different oxidized guanines in different DNA positions. By furthering our understanding of damaged DNA processing by DNA polymerase β, this work expands the current literature of DNA polymerase discrimination mechanisms and informs on the mutagenic properties of formerly uncharacterized damaged DNA substrates.