Component of the PeBoW complex, which is required for maturation of 28S and 5.8S ribosomal RNAs and formation of the 60S ribosome. Component of the PeBoW complex, composed of BOP1, PES1 and WDR12. The complex is held together by BOP1, which interacts with PES1 via its N-terminal domain and with WDR12 via a high-affinity interaction between the seven-bladed beta-propeller domains of the 2 proteins. The PeBoW complex associates with the 66S pre-ribosome. Interacts (via UBL domain) with MDN1 (via VWFA/MIDAS domain). Belongs to the WD repeat WDR12/YTM1 family.