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. WDR40A (WD-repeat-containing protein 40A), also known as DDB1- CUL4-associated factor 12, is a 453 amino acid cytoplasmic protein that contains four WD-repeats. WDR40A is highly expressed in some cancer cell lines, lung cancer tissues and normal testis. A probable substrate receptor for CUL4-DDB1 E3 ubiquitin-protein ligase complex, WRD40A is suggested to interact with DDB1. WDR40A is encoded by a gene mapping to human chromosome 9p13.3. Human chromosome 9 houses over 900 genes and comprises nearly 4% of the human genome.