This domain family is found in eukaryotes, and is approximately 40 amino acids in length. The family is found in association with pfam00227. There is a conserved GTT sequence motif. There is a single completely conserved residue Y that may be functionally important. This family includes the C terminal of the beta-type subunits of the proteasome, a multimeric complex that degrades proteins into peptides as part of the MHC class I-mediated Ag-presenting pathway.