The PFU (for PLAA family ubiquitin binding domain) is an ubiquitin binding domain with no homology to several known ubiquitin binding domains (e.g., UIM, NZF, UBA, UEV, UBP, or CUE domains). The PFU domain appears to be unique to the PLAA family of proteins. A single member of this family of proteins exists in every eukaryotic species examined. Each of these homologues possesses identical domain structure: an N-terminal domain containing seven WD40 repeats, a central PFU domain, and a C-terminal PUL domain, which directly binds to Cdc48, a member of the AAA-ATPase family of molecular chaperone.In addition to ubiquitin, the PFU domain of DOA1 has been shown to bind to the SH3 domain.