Pauklin, S.; (2009) Regulation of activation induced deaminase. Doctoral thesis , UCL (University College London).

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Abstract

Activation Induced Deaminase (AID) belongs to the protein family of DNA deaminases, which catalyse the deamination of the cytosine residues in single stranded DNA, resulting in the formation of deoxy-uracils. The enzymatic activity of AID is required for the immunoglobulin gene modifications by class switch recombination (CSR), somatic hypermutation (SHM) and gene conversion (iGC). While being essential for antibody diversification, the activity of AID can be harmful for the organism due to its direct mutagenic activities and induction of genomic instability. This thesis investigates AID regulation both, on the level of gene expression and its interaction partners, and the DNA repair pathways triggered by AIDmediated DNA deamination. Firstly, I have identified estrogen and progesterone as regulators of AID expression. This is achieved via direct binding of estrogen and progesterone receptors to AID promoter. Estrogen leads to an induction of AID expression and increase in AID-mediated downstream pathways – SHM, CSR as well as oncogenic translocations between Ig and c-myc loci. In contrast, progesterone results in a decrease in AID expression and an attenuation of its downstream pathways. Secondly, by generating DT40 cell lines with endogenously tagged AID, we used co-immunoprecipitation and subsequent mass spectrometry for identifying proteins that form a complex with AID in the cytoplasm, nucleoplasm and chromatin. The results of this approach gave us possible insight into the mechanistic process of AID-mediated DNA deamination in vivo, suggesting that chromatin bound AID resides in a complex with elongating RNA polymerase II. Thirdly, by expressing AID in meiotic recombination deficient fission yeast and nematode, we have established that a meiotic cell can process a base mismatch, using the base excision repair machinery, to give rise to meiotic recombination. This suggests that meiotic cells can process lesions other than Spo-11 induced DSBs for recombination.

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