Skp1 proteins are structural components of the synaptonemal complex in C. elegans

The synaptonemal complex (SC) is a hallmark of meiotic prophase that plays a crucial role in regulating crossovers between homologous chromosomes. Here, we demonstrate that two Skp1-related proteins in C. elegans, SKR-1 and SKR-2, serve as structural components of the SC, independent of their canonical functions within the Skp1-Cul1-F-box (SCF) ubiquitin ligase complex. SKR-1 and SKR-2 localize to the central region of the SC, and synapsis requires their dimerization through a hydrophobic interface that overlaps with the binding sites for CUL-1 and F-box proteins. Using in vitro reconstitution and in vivo analysis of mutant proteins, we show that SKR proteins interact with the other SC proteins using their C-terminal helices to form a soluble complex, which likely represents a basic building block for SC assembly. Our findings demonstrate how conserved Skp1 proteins are repurposed as part of the SC and may provide insight into how synapsis is coupled to cell cycle progression.