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Title: Functional analysis of the DNA repair protein MBD4
Author: MacDougall, Eilidh Fiona
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2006
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The methylation of cytosine plays a fundamental role in mediating transcriptional repression. However, 5-methylcytosine can undergo spontaneous hydrolytic delamination to form thymine. It the resulting T:G mismatch is replicated prior to being repaired, a C:G to T:A transition mutation will be present in one of the two daughter DNA molecules. Methyl-CpG-binding domain protein 4 (MBD4) is a DNA glycosylase that can excise thymine from mismatches with guanine, and that acts preferentially on T:G mismatches within CpG dinucleotides in vitro. In order to test the hypothesis that MBD4 repairs the product of 5-methylcytosine delamination in vivo, MBD4-deficient mice were crossed onto the Big Blue genetic background. This background enables the frequency and spectrum of in vivo mutations in a bacteriophage lambda cII transgene to be determined. As predicted, Mbd4-/- mice have a significantly increased frequency of C:G to T:A mutation sat CpG dinucleotides. T:G mismatch-specific thymine DNA glycosine (TDG) can also attempt to excise thymine from T:G mismatches within CpG dinucleotides in vitro. In an attempt to determine the relative contributions of MBD4 and TDG to the repair of 5-methylcytosine delamination-induced T:G mismatches in vivo, the mutation frequencies and spectra in cell lines lacking MBD4 and/or TDG were measured. An additional line of research focused on potential mechanisms by which the DNA repair activity of MBD4 may be regulated. A novel protein has previously been shown to interact with MBD4 in a yeast two-hybrid screen that used MBD4 as the bait protein. This interaction was further characterised by mapping of the interaction domains using the yeast two-hybrid assay, and by immunocytochemistry. Finally, it was also shown that MBD4 may be post-translationally modified by sumoylation.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available