错配修复蛋白Mlh3对四膜虫有性生殖是必需的

DNA错配修复(mismatch repair, MMR)是一种进化中保守的机制，它校正DNA复制过程中产生的错误，维持基因组的稳定性。MMR家族蛋白同时也参与多种DNA相关的生物学功能。本研究从嗜热四膜虫鉴定了一种新的错配修复蛋白MLH3基因，该基因预测编码 319 个氨基酸，在有性生殖期特异表达。免疫荧光定位表明，HA-Mlh3定位在有性生殖期减数分裂的小核和新发育的大核中。MLH3 敲除的突变体细胞株，在有性生殖发育期停滞在两大核和两小核阶段，新大核DNA复制受阻。γ-H2A.X 检测表明，新大核和小核有性生殖后期断裂的基因组不能正常修复，发育中的细胞裂解，不能形成有性生殖后代。结果表明，Mlh3参与四膜虫新大核发育过程基因组的断裂修复和复制，对四膜虫的有性生殖是必需的。

Mismatch Repair Protein Mlh3 is Required for Conjugation Development in Tetrahymena thermophila

DNA mismatch repair(MMR) is an evolutionarily conserved process that corrects mismatches generated during DNA replication. MMR proteins also play important roles in many other DNA transactions. In this study, mismatch repair protein Mlh3 was identified from Tetrahymena thermophila. MLH3 contains a 957 bp open reading frame and encodes a protein of 319 amino acids. MLH3 was specifically expressed during conjugation stage. Immunofluorescence staining showed that HA-Mlh3 localized in the micronucleus (Mic) and new developing macronucleus (Mac). MLH3 knockout cells arrested in the two Macs and two Mics stage during conjugation stage. DNA replication was also inhibited in the new developing Macs. γ-H2A.X staining showed new Macs and new Mics failed to repair during late conjugation stage and failed to produce sexual progeny. Mating cells were broken during later stage. The results showed that Mlh3 is involved in the new macronuclear genome repair and replication, and Mlh3 is required for conjugation development in T. thermophila.