Msh2 and Mlh1 proteins from Tetrahymena thermophla are homologues of MutS and MutL from Escherichia coli respectively. MutS and MutL are DNA mismatch repair proteins. In eukaryotes, MutS homologues recognize the replication errors and MutL homologues interact with MutS homologues and other proteins to make the repair occur. Biolistic transformation has been done to make the msh2 and mlh1 single knockouts in the macronuclei of different strains and the knockouts were verified complete. Two strains of WT crossing KO or KO crossing KO, with different mating types, were induced to conjugate. The processes were studied by microscopy using DAPI staining. For the msh2 knockouts, there were no crescent micronuclei formed throughout the conjugation of two knockout cells, and the pairing level was reduced severely. However, a knockout cell and a wild-type cell could conjugate normally at a high level pairing efficiency. Msh2 protein seems to be important to cell pairing and indispensible for the formation of the crescent micronuclei during cell conjugation. For the mlh1 knockouts, the pairing level of a knockout and a wild-type was reduced by half and the pairing level of two knockouts was reduced more than 80%; however, the paired cells in both could complete the conjugation with delay. Pms2 protein may have redundant roles in the MutL heterodimer (Mlh1-Pms2). In addition, chemical mutagens treated knockout was crossed with non-treated wild-type and the conjugation was compared with treated wild-types. Most of the treated knockout cells could not pair after starvation and mixing with non-treated wild-type cells, which means most of the cells could not enter meiotic phase. It is probable that G2/M checkpoint arrested the meiotic cell cycle and the intra-S phase was inactivated. Thus, Msh2 protein may have a role in the meiotic intra-S phase checkpoint system.

Dissertation (Ph.D.)--University of Toledo, 2009. / "In partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biomedical Sciences." Title from title page of PDF document. Bibliography: p. 174-180, p. 201-238.

Mismatch repair corrects errors made during DNA replication and inactive mismatch repair is associated with Lynch Syndrome and sporadic cancer. Genome replication in eukaryotes is accompanied by chromatin formation. The first step in chromatin establishment is nucleosome assembly, that starts with histone tetramer deposition. It is not clear how three important cellular processes: genome replication, mismatch repair and nucleosome assembly are coordinated. Here we analyzed human mismatch repair in the presence of histone deposition in a reconstituted system. We showed that mismatch repair factor inhibits nucleosome assembly on the DNA region with the replicative error. Such a mechanism is important, since in this way DNA with errors remains accessible for mismatch repair system to perform the repair. The DNA synthesis step in mismatch repair is performed by DNA polymerase. Eukaryotes possess two major replicative DNA Polymerases: DNA Polymerase delta and DNA Polymerase epsilon. DNA polymerase delta is involved in mismatch repair. However, it was unknown whether DNA polymerase epsilon can also work in mismatch repair. Here we analyzed human mismatch repair with DNA Polymerase delta and DNA Polymerase epsilon in the environment of histone deposition. Our results indicated that repair activity with both polymerases was activated by histone deposition. Here it was first shown that human DNA Polymerase epsilon performs DNA synthesis during mismatch repair in vitro. Importantly, recent studies have revealed association of Polymerase epsilon mutations with cancer. Since our data showed activity of DNA Polymerase epsilon in mismatch repair, a possible tumor development mechanism may involve inactivation of mismatch repair due to Polymerase epsilon mutations. Overall, our study expanded the understanding of the mechanism of human mismatch repair in the chromatin environment.

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第18110号 / 理博第3988号 / 新制||理||1575(附属図書館) / 30968 / 京都大学大学院理学研究科生物科学専攻 / (主査)准教授 秋山 秋梅, 教授 沼田 英治, 教授 疋田 努 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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DNA mismatch repair ensures faithful transmission of genetic material from parents to progeny, which is required for the survival of the organism. The studies on E. coli MMR proteins have formed the basis for the study of the MMR system in eukaryotic organisms, because the functions of MMR proteins believed to be been conserved. In organisms that harbor MutH protein, it is known that MutH acts as a monomer which nicks the unmethylated daughter strand and is activated in a MutS-MutL- dependent manner. The cleavage specificity of MutH is very stringent. Till recently, it was not clear as to how MutH distinguishes hemimethylated DNA from fully or unmethylated DNA. The co-crystal structures of MutH-DNA complexes revealed that Y212, R184 and P185 were in close proximity to the methyl-adenine. Clustal-W sequence alignment of MutH with Sau3AI showed that Sau3AI has PCT residues instead of L183, R184, and P185. A triple mutant MutH-L183P-R184C-P185T was found to cleave both unmethylated and methylated DNA. The nicking endonuclease activity of the LRP→ PCT triple mutant was enhanced in the presence of Haemophilus influenzae MutL. The mutL gene of Neisseria gonorrhoeae was cloned and the gene product purified. It was shown that the homodimeric Neisseria gonorrhoeae MutL (NgoL) protein displays an endonuclease activity that incises covalently closed circular DNA in the presence of manganese or magnesium or calcium ions unlike human MutLα which shows endonuclease activity only in the presence of manganese. Further more the C-terminal domain of Neisseria gonorrhoeae MutL (NgoL-CTD) consisting of amino acids 460 to 658 also exhibits Mn2+ dependent endonuclease activity. Sedimentation velocity, sedimentation equilibrium and dynamic light scattering experiments show NgoL-CTD to be a dimer. By in vitro comparison of wild-type and a mutant NgoL-CTD protein, it was shown that the latter protein exhibits highly reduced endonuclease activity. Surface plasmon resonance spectroscopy was used to determine the kinetics of DNA binding by NgoL. The DNA binding was carried out in absence of metal ions. Interaction studies with NgoL with ssDNA in SPR spectroscopy revealed a KD value of 4.7 × 10–8 M. While the human MutLα endonuclease activity was shown to be stimulated by ATP, ATP inhibits NgoL endonuclease activity. By in vitro comparison of wild-type and a mutant NgoL-CTD protein, it was shown that the latter protein exhibits highly reduced endonuclease activity. NgoL ATPase activity was enhanced in the presence of DNA. The fact that NgoL ATPase activity is stimulated ~ 2.5-fold by dsDNA and ~ 2-fold by ssDNA is a further evidence for the interaction between NgoL and DNA. The results presented above show that NgoL harbors a nicking endonuclease activity which is present in the C-terminal domain. NgoL and NgoL-CTD are dimers in solution and DMHA(X)2E(X)4E motif present in the CTD is required for the nicking endonuclease activity. These results suggest that DNA mismatch repair mechanism in N. gonorrhoeae is different from that in E. coli. In the absence of MutH homolog, N. gonorrhoeae is able to repair the DNA by virtue of MutL nicking endonuclease activity.

No description available.

A queilite actínica (QA) é o resultado da exposição crônica dos lábios à radiação ultravioleta do sol. É considerada uma lesão cancerizável e calcula -se que cerca de 10% a 20% evoluirão para carcinoma epidermóide. Já foi sugerido que virtualmente todos os carcinomas epidermóides de lábio (CEL) iniciem como QA. Sabe-se que as radiações solares têm a capacidade de alterar o DNA e que, nesse contexto, os genes de reparo de DNA têm papel fundamental em reparar essas alterações e limitar os danos causados. Porém, estes genes também podem ser vítimas das radiações ultravioletas do sol. O objetivo deste trabalho foi estudar a participação dos genes de reparo de mau pareamento (RMP) do DNA em QA de diferentes graus de atipia e comparar os achados ao carcinoma de lábio relacionado à QA. Para tanto, foram analisadas nestas lesões a expressão e distribuição das proteínas codificadas por dois destes genes, hMLH1 e hMSH6, através da imunoistoquímica. Foi observado que a expressão das duas proteínas diminuía de acordo com o agravamento da indiferenciação celular das lesões. A partir disto, pode-se concluir que a diminuição na expressão de hMLH1 e hMSH6 parece estar relacionada com a progressão do grau de atipia nas QA, e, conseqüentemente, com a tumorigênese do CEL. Além disso, a proteína hMSH6 não pareceu ter um papel importante no reparo do DNA do epitélio labial normal. / Actinic cheilitis (AC) results from chronic and excessive exposure of the lips to the ultraviolet radiation in sunlight. AC is recognized as a potentially malignant condition and it is estimated that 10% to 20% will become lip squamous cell carcinoma (LSCC). It has been suggested that virtually every LSCC was initially AC. It is well known that solar radiation causes DNA damage and, in this context, the DNA repair systems play an extremely important role in restoring the injuries. The purpose of this study was to evaluate the participation of the mismatch repair (MMR) system in AC with all grades of dysplasia, as well as, LSCC related to AC. The protein expression and distribution of two of these genes, hMLH1 and hMSH6 were analyzed by means of immunohistochemistry. The results have shown an association between decreased expression of hMLH1 and hMSH6 proteins and the progression of the dysplasia in AC and, therefore, LSCC carcinogenesis. In addition, the hMSH6 protein does not seem to have a primary role in DNA repair of the normal lip epithelium.