InterPro domain: IPR003126

It has been observed that the identity of N-terminal residues of a protein isrelated to the half life of the protein. This observation yields a rule,called the N-end rule [ 1 ]. Similar but distinct versions of the N-end rule operate in all organisms examined, from mammals to fungi and bacteria. Ineukaryotes, the N-end rule pathway is a part of the ubiquitin degradationsystem. Some proteins that have a very short half life contain a specificmotif at their N terminus, the N-degron. It consists of a destabilisingN-terminal residue and an internal Lys, which is the site of poly-Ub chain[ 2 , 2 ].

The UBR1 protein was shown to bind specifically to proteins bearing N-terminalresidues that are destabilising according to the N-end rule, but not tootherwise identical proteins bearing stabilising N-terminal residues [ 3 ]. UBR1 contains an N-terminal conserved region (the UBR-type zinc finger) which is also found in various proteins implicated in N-degron recognition. The UBR-type zinc finger defines a unique E3 class, most likely N-degron specific [ 4 ].

1. The N-end rule: functions, mysteries, uses. Proc. Natl. Acad. Sci. U.S.A. 93, 12142-9
2. Degradation signals in the lysine-asparagine sequence space. EMBO J. 18, 6017-26
3. The E2-E3 interaction in the N-end rule pathway: the RING-H2 finger of E3 is required for the synthesis of multiubiquitin chain. EMBO J. 18, 6832-44
4. A family of mammalian E3 ubiquitin ligases that contain the UBR box motif and recognize N-degrons. Mol. Cell. Biol. 25, 7120-36