SUMO E3 ligase that acts as a regulator of crossing-over during meiosis: required to couple chromosome synapsis to the formation of crossover-specific recombination complexes. Localizes to recombination sites and stabilizes meiosis-specific recombination factors, such as MutS-gamma complex proteins (MSH4 and MSH5) and TEX11. May mediate sumoylation of target proteins MSH4 and/or MSH5, leading to enhance their binding to recombination sites. Acts as a limiting factor for crossover designation and/or reinforcement and plays an antagonist role with CCNB1IP1/HEI10 in the regulation of meiotic recombination (By similarity). Protein modification; protein sumoylation. Associates to the synaptonemal complex. Localizes to a minority of double-strand breaks (DSBs) sites. Marks crossover sites during midpachynema (By similarity). Genetic variations in RNF212 influence recombination rate, designated recombination rate quantitative trait locus 1 (RRQTL1) [MIM:612042].