Graduate Thesis Or Dissertation
 

Functional analysis of the pathogenic mutation MLH1-E578G on human MLH1 activity in DNA mismatch repair

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  • Mismatch repair (MMR) system performs mainly three roles to maintain genomic stability, correct DNA biosynthetic errors, ensure the fidelity of genetic recombination, and in mammalian cells participate in the cellular response to some DNA damages. Deficiencies in mismatch repair increase mutation rates and cancer risks. In eukaryotes, the MMR system contains several MSH (MutS homolog) and MLH (MutL homolog) proteins. Some germline mutations in human mismatch repair genes, mainly MSH2 and MLH1, have been found to be associated with Lynch Syndrome (as known as HNPCC, hereditary non-polyposis colorectal cancer). In this study, I examined the effect of a pathogenic mutation MLHI-E578G on MLH1-deperident error correction on base-base mismatch and dinucleotide loop. I conducted in vitro repair assay utilizing cell lines that express either wild-type or mutant MLH1 protein, and the 3 'mismatched DNA substrates. I successfully applied cytoplasmic extracts in in vitro repair assays, which might provide an easy way for studying other protein functions in human and mouse cell lines. By comparing the repair efficiency of base-base and dinucleotide loop DNA by both mutant and wild type MLH1, I found that the repair activity is dependent on MutLa concentration. In a 15-minute reaction, the mutant protein MLII 1-E578G can support the repair of C-loop, CT-loop and GIT mismatch as well as wild-type MLH1. As suggested by the kinetics experiment, the in vitro MMR reactions are saturated at about 10 minutes; so a shorter time reaction time might be the best for in vitro repair comparisons. To have a better understanding of how MLHI-E578G contributes to an increased risk of disease, further studies need to be done.
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