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Download or read book Interhomolog Bias and the Recombination Checkpoint During Meiosis written by Hsuan-Chung Ho and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Meiotic recombination is required for faithful chromosome segregation during meiosis I. Meiotic cells utilizes the repair of deliberately-introduced DNA double-strand breaks (DSBs) to connect homologous chromosomes physically by crossover recombination. These programmed DSBs must be repaired in a timely fashion to ensure genome integrity (meiotic recombination checkpoint). In addition, these breaks must be repaired using homologous non-sister chromatids (interhomolog bias) to achieve connections between homologous chromosomes. The aim of this dissertation was to investigate these important meiotic processes by studying (i) a meiosis-specific checkpoint kinase Mek1, and (ii) a meiosis-specific AAA-ATPase Pch2 in budding yeast Saccharomyces cerevisiae. (i) We analyzed a MEK1 gain-of-function allele expressing Mek1-GST whose activation is artificially maintained through GST-mediated dimerization. MEK1-GST results in enhanced interhomolog bias. Ectopic Mek1 dimerization is also sufficient to impose interhomolog bias in the absence of recombination checkpoint functions, thereby uncoupling these two processes. In addition, the stringency of the checkpoint response is enhanced in mutants with weak recombination defects by blocking prophase exit in a subset of cells in which arrest is not absolute. We propose that Mek1 plays dual roles during meiotic prophase I by phosphorylating targets directly involved in the recombination checkpoint, as well as targets involved in inhibiting intersister recombination. (ii) We investigated a role for Pch2 in regulating interhomolog bias and the meiotic recombination checkpoint in response to unprocessed DSBs through the activation of axial proteins Hop1 and Mek1. Pch2 physically interacts with the putative BRCT repeats in the N-terminal region of Xrs2, a member of the MRX complex that acts at sites of unprocessed DSBs. Pch2, Xrs2 and the ATM ortholog Tel1 function in the same pathway leading to the phosphorylation of Hop1, independent of Rad17 and the ATR ortholog Mec1, which respond to the presence of single-stranded DNA. An N-terminal deletion of Xrs2 recapitulates several pch2[delta] phenotypes. We propose that interaction with Xrs2 may enable Pch2 to remodel chromosome structure adjacent to the site of a DSB to promote accessibility of Hop1 to the Tel1 kinase. In addition, Xrs2, like Pch2, is required for checkpoint-mediated delay conferred by the failure to synapse chromosomes.