Abstract: The half-life of a Type I, II and III non-compartmentalized intracellular proteins is increased in living eukaryotic cells by contacting the cells with a regulator having an amino-terminal amino acid residue which is the same or similar to the amino-terminal residue of the intracellular protein. The regulator is a dipeptide, a small polypeptide or a carboxyl-terminal derivative of an amino acid. The dipeptide or small polypeptide has an N-terminal amino acid residue which is Arg, Lys or His for the Type I protein, Phe, Leu, Trp, Tyr or Ile for the Type II protein and Ala, Ser or Thr for the Type III protein. The carboxyl-terminal derivative of an amino acid may be an amino acid modified at its C-terminus by the addition of a group selected from methyl, ethyl, propyl, butyl and isobutyl. The amino acid modified is the N-terminal amino acid residue of the dipeptide or small polypeptide for the respective Type I, II and III proteins.

Abstract: This invention pertains to a method of metabolically destabilizing a protein or peptide of interest in vivo provided that the protein or peptide contains a second determinant of the N-end rule-based degradation signal and provided that another (targeting) protein or peptide can be identified that specifically interacts with the protein or peptide of interest. The methods of the invention comprise contacting the protein or peptide of interest with the targeting protein or peptide which contains a destabilizing amino-terminal amino acid according to the N-end rule of protein degradation but lacking a second determinant of the N-end rule-based degradation signal. Because nearly all proteins specifically interact with other proteins, this is a broadly applicable method for metabolically destabilizing a protein or peptide of interest in vivo.