Synaptonemal complex assembly in yeast depends on a 2:2 Ecm11-Gmc2 heterocomplex

Synaptonemal complex (SC) is a structurally conserved, supramolecular assembly that forms at the interface of aligned chromosome axes during meiosis, where it provides a physical context for crossover recombination intermediates. In yeast, the SC is composed of Zip1 transverse filaments and central element proteins Ecm11 and Gmc2. Here, we identify a biochemically stable constitutive complex between Ecm11 and Gmc2, which is mediated by their α-helical coiled-coil regions formed of amino acids 230-302 and 59-188, respectively. We find that the Ecm11-Gmc2 is a 2 : 2 hetero-oligomer, which has an architecture and dimensions similar to the mammalian SC central element complex SYCE2-TEX12. Through targeted mutagenesis in yeast, we show that 2 : 2 Ecm11-Gmc2 complex formation is essential for SC assembly in vivo. Further, we identify key additional residues, particularly in Ecm11, that are dispensable for heterocomplex formation in vitro but critical for stability of the complex in vivo.