PRE3, HIGHLY HOMOLOGOUS TO THE HUMAN MAJOR HISTOCOMPATIBILITY COMPLEX-LINKED LMP2 (RING12) GENE, CODES FOR A YEAST PROTEASOME SUBUNIT NECESSARY FOR THE PEPTIDYLGLUTAMYL-PEPTIDE HYDROLYZING ACTIVITY

20S proteasomes are multifunctional proteinase complexes ubiquitous in eucaryotes. We have cloned the yeast PPE3 gene by complementation of the pre3-2 mutation, which leads to a defect in the peptidylglutamyl-p eptide hydrolyzing activity of the 20S proteasome. The PRE3 gene, a be ta-type member of the proteasomal gene family, is essential for cellul ar life and codes for a 193-amino acid proteasomal subunit with a pred icted molecular mass of 21.2 kDa. The Pre3 protein shows striking homo logy to the human proteasome subunits Hsdelta and Lmp2 (Ring12). Lmp2 is encoded in the major histocompatibility complex class II region imp licating proteasomes in antigen processing.