DNA base excision repair : mutation induction and novel functions
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Original versionDNA base excision repair : mutation induction and novel functions by Izaskun Muruzábal‐Lecumberri, Stavanger : University of Stavanger, 2015 (PhD thesis UiS, no. 258)
DNA is susceptible to chemical modifications corrupting its cellular information processing function, necessitating correction of such modifications. Cells are formed mostly by water – giving rise to hydrolytic reactions – and aerobic metabolism is a source of reactive oxygen species (ROS) – causing oxidation. Deamination of cytosine to uracil is an example of the former and oxidation of thymine to 5-formyluracil (f5U) is an example of the latter. In order to avoid the incorporation of wrong nucleosides into DNA, f5U must be eliminated and substituted by the correct base. The main mechanism for the repair of f5U is the base excision repair (BER) pathway, in which specific glycosylases recognize the damage and excise it from its ribose residue. Several glycosylases have been found to be involved in the repair of f5U in Escherichia coli, where 3-methyladenine DNA glycosylase II (AlkA) may be the most mportant. However, here we present evidence to indicate that the nucleotide excision repair protein UvrA is also involved in the repair of f5U, although the mechanism has yet to be elucidated. Interestingly, we have found that the AlkA glycosylase, in addition to alleviating is also able to promote mutation induction by 5-formyldeoxyuridine in E. coli. Extrapolated to the mammalian system this observation suggests that DNA repair genes may act as oncogenes under certain cellular conditions. Uracil lesions in DNA are repaired by the BER pathway initiated by a monofunctional uracil-DNA glycosylase (UDG), and the family 1 UDGs are the most extensively studied glycosylases. We have found that UDG-mediated repair initiation by E. coli Ung and hUNG also involves DNA strand incision generating a 3’-α,β-unsaturated aldehyde (UIP) and a 5’-phosphate, which demonstrates that they are indeed bi-functional enzymes. However, while the cleavage of the N-glycosol bond by β-elimination occurs through a covalent Schiff base intermediate between a reactive active site lysine and the deoxyribose moiety in other bi-functional glycosylases, the uracil–deoxyribose bond is suggested to be cleaved by an activated water molecule carrying out the elimination reaction.
Contains the introduction. The papers are not included for copyright reasons.
Has partsPaper 1: Marina Alexeeva, Marivi N. Moen, Xiang Ming Xu, Kristin Grøsvik, Izaskun Muruzábal-Lecumberri, Kristine M. Olsen, Ingar Leiros, Finn Kirpekar, Arne Klungland and Svein Bjelland: DNA uracil excision includes strand incision by hUNG. Manuscript.
Paper 2: Kristin Grøsvik, Izaskun Muruzábal-Lecumberri and Svein Bjelland: Severe repair-deficiency for oxidised DNA bases causes primarily G·C → A·T transitions in Escherichia coli. Manuscript.
Paper 3: Kristin Grøsvik, Izaskun Muruzábal-Lecumberri, Ingeborg Knævelsrud, Gyri Teien Haugland, Hilde Ånensen, Ingrun Alseth, Kousuke Sato, Akira Matsuda, Ingar Leiros, Arne Klungland and Svein Bjelland: Damage-specific mutation induction promoted by repair. Manuscript.
Paper 4: Izaskun Muruzábal-Lecumberri, Kristin Grøsvik, Kousuke Sato, Akira Matsuda and Svein Bjelland: Alleviation and promotion of damage-specific mutation induction in Escherichia coli are highly dependent on the uvrA gene. Manuscript.