WD-repeats are motifs that are found in a variety of proteins and are characterized by a conserved core of 40-60 amino acids that commonly form a tertiary propeller structure. While proteins that contain WD-repeats participate in a wide range of cellular functions, they are generally involved in regulatory mechanisms concerning chromatin assembly, cell cycle control, signal transduction, RNA processing, apoptosis and vesicular trafficking. UTP18 (U3 small nucleolar RNA-associated protein 18), also known as WDR50 (WD repeat-containing protein 50), is a 556 amino acid protein that localizes to the nucleus, contains six WD repeats and is thought to be involved in the processing of pre-18S ribosomal RNA. The gene encoding UTP18 maps to human chromosome 17, which comprises over 2.5% of the human genome and encodes over 1,200 genes.