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Amy J. MacQueen; Scott Holmes; Manju Hingorani


Molecular Biology and Biochemistry




Prior to crossover formation during meiosis I, homolog pairing and double-strand break repair processes promote synaptonemal complex, SC, formation along the axial length of the paired chromosomes. The SC is a widely conserved, proteinaceous structure that assembles between lengthwise-aligned homologs and regulates the level of crossover recombination events and their distribution. The SC is established through the multimeric assembly of coiled-coil containing transverse filament proteins along with other protein components. The small ubiquitin-like modifier protein, SUMO, localizes to Saccharomyces cerevisiae SC in a Zip1-dependent manner, but its role in SC assembly or function is unknown. We investigated the potential role of SUMO in SC assembly and function. To diminish SUMO in meiotic prophase cells, we created a diploid strain trans-heterozygous for a deletion in SMT3, the gene encoding SUMO, and an SMT3 gene driven by the vegetative promoter, PSCC1. Through this “less-of-function” approach, we observed that SUMO-diminished cell lines exhibit reduced sporulation efficiency and undergo an arrest at late meiotic prophase. Moreover, we observed that Zip1 infrequently assembles extensive, continuous stretches on meiotic prophase chromosomes in SUMO-diminished nuclei, unlike control nuclei. Thus, Zip1 and SUMO are mutually dependent for assembling mature SC structure. We also created a strain carrying an inducible, V5-tagged version of SUMO. With this strain we demonstrated that SUMO incorporates continuously into full length SC during meiotic prophase progression, similar to the dynamics of the transverse filament protein, Zip1. Using Structured Illumination microscopy, we also show that SUMO localizes near the N termini of Zip1 within the central element of the SC, in contrast to current models of SC architecture. Our observations are consistent with a structural role for SUMO (or its SC SUMOylated substrate) in building the budding yeast SC.



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