This domain is found in eukaryotes, and is approximately 40 amino acids in length. It is found associated with pfam00646, pfam00400. The protein that contains this domain functions as a ubiquitin ligase. Ubiquitination is required to direct proteins towards the proteasome for degradation. This protein is part of the WD40 class of F box proteins. The D domain of these F box proteins is involved in mediating the dimerization of the protein. dimerization is necessary to polyubiquitinate substrates so this D domain is vital in directing substrates towards the proteasome for degradation.