The CUE family was first described as a region of homology between the yeast Cue1 (coupling of ubiquitin to ER degradation) and human Tollip proteins. The domain is approximately 40 amino acids in length and is found in proteins that have a variety of functions, including the degradation of misfolded proteins in the endoplasmic reticulum and protein sorting. CUE domains have been shown to both bind mono and polyubiquitin and some CUE domain-containing proteins are themselves ubiquitinylated in a CUE domain-dependent manner (1).

1. http://www.cellsignal.com/contents/resources-protein-domains-interactions/cue-protein-domain/domains-cue/