Thesis (Ph.D.)--Cornell University, February, 2010. / Includes bibliographical references.

Thesis (Ph.D.)--University of Wisconsin--Madison, 2006. / Description based on print version record. Includes bibliographical references (p. 405-431).

Thesis (Ph. D.)--University of Wisconsin--Madison, 1995. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 119-128).

Thesis (Ph.D.)--University of Delaware, 2007. / Principal faculty advisor: Eric B. Kmiec, Dept. of Biological Sciences. Includes bibliographical references.

No description available.

The mismatch repair system (MMR) is an important pathway for maintaining genome stability because it can remove the errors generated while the cell is replicating. If these errors are left uncorrected, they can lead to genomic mutations. Thus, the deficient mismatch repair system is associated with the development of sporadic cancers and degenerative diseases such as Lynch Syndrome. MMR involves a set of proteins including MutSα, MutLα, MutLβ, and MutLγ. MutSα and MutLα play a major role in MMR whereas MutLβ and MutLγ provide minor contributions to this pathway. Recent studies have suggested that MutLβ and MutLγ are involved in the triplet DNA repeat expansion pathway. Our study in Saccharomyces cerevisiae shows important preliminary data of Mlh3 in maintaining genomic stability. We studied its interactions with other proteins involved in the mismatch repair system. Interestingly, Mlh3 interactions with Msh3 and Pol 35 DV suggest that there is a predilection of MutSβ and MutLγ to work in the lagging strand. Additionally, Top1, Mlh3and Msh3our results have shown that these genetic interactions could lead to an increase in mistakes in the MMR pathway. Moreover, it could lead to the suggestion that they are also involved in another pathway such as transcription. Finally, we confirm the involvement of Mlh3 in the resolution of frameshift mutations in the His-7A locus. Even though they are interesting results is too early to make final conclusions. Further analysis needs to be done.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal.

Mémoire numérisé par la Division de la gestion de documents et des archives de l'Université de Montréal

碩士 / 國立陽明大學 / 微生物暨免疫學研究所 / 88 / IS1372, a member of IS3 family, is a 1,304 bp transposable element of Streptomyces lividans. IS1372 contains two open reading frames, named orfA and orfB, respectively. In our lab’s previous study, we investigated the gene products of IS1372 by T7 RNA polymerase system in E. coli. Three proteins were expressed, including InsA (14 kDa), 0 frame product of orfA, InsAB’ (42 kDa), orfA fused with orfB by —1 frameshift, and unexpected, InsAB” (18 kDa), +1 frameshift of orfA. Since there is no previous report about the transposable elements of IS3 family can generate a +1 frameshift product besides the known —1 frameshift product, it is our major topic to study on the production of InsAB’ and InsAB”, and the mechanism of frameshift. There is no report about two frameshift signals could exist in a transposable element, but —1 and +1 frameshift events may occur on the same signal (Brierley et al., 1992). We suggested that the —1 and +1 frameshifts might occur on the same putative frameshift signal, T6G, of IS1372. After we mutated T6G to GATATCG, the efficiency of —1 frameshift became undetectable, but it had no effect on the +1 frameshift. Therefore, T6G might be the signal of —1 frameshift but not +1 frameshift. On the other hand, there are also reports about the stimulation of +1 frameshift by hungry codon. To investigate the relationship between +1 frameshift and hungry codon, we added extra copies of tRNAs that decodes hungry codons into cells, we found that the efficiency of +1 frameshift decreased in these cells. Then we mutated the hungry codon of 465AGG to CGT, which also encodes arginine with higher codon usage in E. coli, the efficiency of +1 frameshift decreased. Therefore, the +1 frameshift of IS1372 might occur on the signal of ACG-AGG-C, which is in downstream of T6G. Two frameshift products of IS1372 were expressed in E. coli is novel in the gene expression of transposable elements. However, the existences and biological functions of these two frameshift products of IS1372 in the original host S. lividans remains further investigation.

No description available.