The ubiquitin-specific protease family from arabidopsis. AtUBP1 and 2 are required for the resistance to the amino acid analog canavanine

Ubiquitin-specific proteases (UBPs) are a family of unique hydrolases that specifically remove polypeptides covalently linked via peptide or isopeptid e bonds to the C-terminal glycine of ubiquitin. UBPs help regulate the ubiq uitin/26S proteolytic pathway by generating free ubiquitin monomers from th eir initial translational products, recycling ubiquitins during the breakdo wn of ubiquitin-protein conjugates, and/or by removing ubiquitin from speci fic targets and thus presumably preventing target degradation. Here, we des cribe a family of 27 UBP genes from Arabidopsis that contain both the conse rved cysteine (Cys) and histidine boxes essential for catalysis. They can b e clustered into 14 subfamilies based on sequence similarity, genomic organ ization, and alignments with their closest relatives from other organisms, with seven subfamilies having two or more members. Recombinant AtUBP2 funct ions as a bona fide UBP: It can release polypeptides attached to ubiquitins via either alpha- or epsilon -amino linkages by an activity that requires the predicted active-site Cys within the Cys box. From the analysis of T-DN A insertion mutants, we demonstrate that the AtUBP1 and 2 subfamily helps c onfer resistance to the arginine analog canavanine. This phenotype suggests that the AtUBP1 and 2 enzymes are needed for abnormal protein turnover in Arabidopsis.