>PF08145 BOP1NT: BOP1NT (NUC169) domain; InterPro: IPR012953 WD-40 repeats (also known as WD or beta-transducin repeats) are short ~40 amino acid motifs, often terminating in a Trp-Asp (W-D) dipeptide
WD40 repeats usually assume a 7-8 bladed beta-propeller fold, but proteins have been found with 4 to 16 repeated units, which also form a circularised beta-propeller structure. WD-repeat proteins are a large family found in all eukaryotes and are implicated in a variety of functions ranging from signal transduction and transcription regulation to cell cycle control and apoptosis. Repeated WD40 motifs act as a site for protein-protein interaction, and proteins containing WD40 repeats are known to serve as platforms for the assembly of protein complexes or mediators of transient interplay among other proteins. The specificity of the proteins is determined by the sequences outside the repeats themselves. Examples of such complexes are G proteins (beta subunit is a beta-propeller), TAFII transcription factor, and E3 ubiquitin ligase [, ]. In Arabidopsis spp., several WD40-containing proteins act as key regulators of plant-specific developmental events. This N-terminal domain is found in BOP1-like WD40 proteins. Bop1 is a nucleolar protein involved in rRNA processing, thereby controlling the cell cycle []. It is required for the maturation of the 25S and 5.8S ribosomal RNAs. It may serve as an essential factor in ribosome formation that coordinates processing of the spacer regions in pre-rRNA. The Pes1-Bop1 complex has several components: BOP1, GRWD1, PES1, ORC6L, and RPL3 and is involved in ribosome biogenesis and altered chromosome segregation. The overexpression of BOP1 increases the percentage of multipolar spindles in human cells. Deregulation of the BOP1 pathway may contribute to colorectal tumourigenesis in humans []. Elevated levels of Bop1 induces Bop1/WDR12 and Bop1/Pes1 subcomplexes and the assembly and integrity of the PeBoW complex is highly sensitive to changes in Bop1 protein levels []. Nop7p-Erb1p-Ytm1p, found in yeast, is potentially the homologous complex of Pes1-Bop1-WDR12 as it is involved in the control of ribosome biogenesis and S phase entry. The integrity of the PeBoW complex is required for ribosome biogenesis and cell proliferation in mammalian cells []. In Giardia, the species specific cytoskeleton protein, beta-giardin, interacts with Bop1 []. ; GO: 0006364 rRNA processing, 0005634 nucleus