FIGURE 1: Mutual activation between Ecm11 SUMOylation and transverse filament assembly shapes the synaptonemal complex. We propose the following model regarding the mechanism forming the synaptonemal complex (SC). First, the transverse filament protein (Zip1) and the assembly activation factor (Ecm11/Gmc2) are independently recruited to a synapsis initiation site. Recruited Zip1 starts to assemble in conjugation with Ecm11/Gmc2, which promotes SUMOylation of Ecm11. This ignites the positive feedback loop, leading to further assembly of Zip1, loading of Ecm11/Gmc2 and SUMOylation of Ecm11 until the SC is fully established.