| Summary: | 碩士 === 國立臺灣大學 === 植物學研究所 === 89 === The yeast meiosis-specific protein Zip1 is a major structural component of the central region of the synaptonemal complex (SC). In the absence of Zip1, chromosomes fail to synapse and recombination intermediates (Holliday junctions) accumulate, resulting in checkpoint-mediated arrest at the pachytene stage of prophase. YGR042w, an unidentified yeast ORF, was previous isolated as a multicopy suppressor of zip1in sporulation, and was named as MSZ1. When MSZ1 is overexpressed in zip1 mutants, sporulation is partially restored. Using epitope-tagging method, the Msz1 protein was detected by Western blot analysis. The result of time course analysis indicated that Msz1 is not a meiosis-specific protein, but its expression is induced in meiosis and peaks around pachytene.
Based on the amino-acid sequence analysis, Msz1 has homology with some chromosome-associated proteins. To verify if Msz1 is also associated with chromosomes, immunolocalization experiments were performed. The results of cytological analyses indicated that the Msz1 protein is a nuclear protein. It is localized to pachytene chromosomes as distinct foci. The chromosomal localization of Msz1 provides an important clue for the study of Msz1 function(s) and pachytene checkpoint machinery. Additionally, when RAD54, a gene involved in sister-chromatid recombination, is deleted in zip1 cells overproducing Msz1, the sporulation frequency was greatly reduced. This result suggests that sister-chromatid repair appears to be involved in the Msz1-mediated suppression pathway.
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