How Do Synaptonemal Complex Proteins Promote Crossover Recombination and Synapsis?

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Project Summary Our proposed research aims to decipher the molecular mechanisms that underlie homologous chromosome segregation during reproductive cell formation. Meiosis is the specialized cell division cycle that partitions the two homologous copies of every chromosome (homologs) to separate daughter nuclei, effectively reducing chromosome ploidy. Errors in chromosome segregation lead to aneuploid reproductive cells that carry too many or two few chromosomes. Key to the success of homolog segregation is the prior establishment of transient but stable associations between replicated chromosomes; for most organisms these links are formed by interhomolog crossover recombination events, in conjunction with intact sister cohesion. How crossover events are efficiently generated between every chromosome pair during meiosis remains poorly understood, but for most organisms it is clear that the process involves an exquisite coordination between large-scale chromosome movements and local DNA repair processes. A conserved multi-protein structure, the synaptonemal complex (SC), mediates an intimate alignment between homologous partner chromosome axes and forms the physical context in which DNA repair intermediates mature. SC has long been associated with successful crossover recombination, and although our recent research demonstrated that the SC structure per se is dispensable for crossing over in budding yeast, we also showed that the SC building block component, Zip1, has a genetically separable function in promoting crossovers. Our structure-function analysis revealed adjacent domains within Zip1’s N terminus that function independently to promote crossover recombination and SC assembly, potentially through separately interfacing with the pro-crossover E3 SUMO ligase, Zip3, and the SC central element protein complex Ecm11-Gmc2. Our recent data has i) revealed a potential phosphorylation-based switch in Zip1’s N terminus that controls its crossover activity, ii) identified several regions within the Zip3 protein required for its pro-recombination and/or pro-SC assembly activities, iii) narrowed the minimal interaction interface between Ecm11 and Gmc2, and iv) demonstrated proximity labeling interactions between pro-crossover proteins (and possibly SC central element proteins) that are stabilized by Zip1’s N terminus. Our proposed experiments, which are designed to support a uniquely rich training environment for several undergraduates, a new “5th year” Masters student, and one doctoral student, build upon our recent experimental data and aim to deepen our structural and functional understanding of the molecular mechanisms that coordinate recombination and SC assembly in S. cerevisiae.