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 (PubMed:15225545). 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 (By similarity). The PeBoW complex also associates with DDX27, PES1 interacts directly with DDX27 (By similarity). Interacts with IRS1 and UBTF (PubMed:15169904). May interact with MAP1B (PubMed:17308336). Appears to localize to the periphery of metaphase chromosomes during mitosis and to the prenucleolar bodies that form in mitotic cells prior to the actual nucleoli. Ubiquitous. Highest levels appear to be found in tissues that contain a population of proliferating cells, such as ovary and testis. Also appears to be highly expressed in kidney and liver. In the brain expression is restricted to neural progenitor cells and postmitotic neurons. Highly expressed in malignant astrocytes. In 2-cell and 4-cell stage interphase blastomeres expression is restricted to a sub-nuclear band that encircles one or more large vacuoles within the nucleus. These vacuoles may give rise to the mature nucleolus. Later in embryogenesis high levels are detected in developing liver. Is also widely and highly expressed throughout the developing brain and spinal cord at embryonic day 13. Induced in malignant astrocytes following the loss of p53. Induced in hepatocytes following partial hepatectomy. Sumoylated. Embryos die during preimplantation stages of development, with blastomeres failing to progress past morula stages. Within blastocysts the nucleoli fail to form correctly and the number of ribosomes appears dramatically reduced. Belongs to the pescadillo family.