How histone H2A monoubiquitination (H2Aub1) is established at specific genomic locations remains unclear. Here, the authors report that Arabidopsis cohesin subunits SCC3 and SYN4 are involved in H2Aub1 through their direct or indirect interaction with BMI1A/B/C subunits of PRC1, the E3 ligases in PRC1 for H2Aub1.
