Visualizing DNA polymerase iota catalyze Hoogsteen-directed DNA synthesis

DNA is constantly damaged by both exogenous and endogenous sources. This damage interferes with normal DNA replication and leads to genome instability. When the replication fork encounters DNA damage in the template strand, the replicative polymerases stall. To overcome these replication blocks, cells are equipped with multiple pathways to bypass the damage. One pathway is Translesion Synthesis, which utilizes polymerases that have evolved to specifically incorporate nucleotides across DNA lesions. The research presented in this thesis focuses on DNA polymerase iota. Vertebrates evolved DNA polymerase iota to accurately incorporate across minor groove and exocyclic purine adducts. Conventional X-ray crystallography showed that this enzyme accommodates damaged adenines and guanines by rotating the template base from the anti to the syn configuration forming Hoogsteen base pairs with the incoming nucleotide. In contrast, polymerase iota is highly inaccurate when incorporating across template pyrimidines. Thus, to prevent mutations, it is vital that the cell utilizes polymerase iota only for its cognate lesions.