The UBR Domain of Plant Ubr1 Homolog PRT6 Accommodates Basic and Hydrophobic Amino Termini for Substrate Recognition.

N-degrons are amino-terminal degradation signals. Non-acetylated first residues with bulky side chains were the first discovered N-degrons. In yeast, their ability to destabilize a protein depends on ubiquitin ligase Ubr1, which has a binding site for basic first residues, the UBR box, and one for hydrophobic first residues, the N domain.