Inhibition of the N-end rule pathway in living cells.

The N-end rule relates the metabolic stability of a protein to the identify of its amino-terminal residue. Previous work, using amino acid derivatives such as dipeptides to inhibit N-end rule-mediated protein degradation in an extract from mammalian reticulocytes, has demonstrated the existence of specific N-end-recognizing proteins in this in vitro system. We now show that these nontoxic amino acid derivatives, when added to growing cells of the yeast Saccharomyces cerevisiae, are able to inhibit the degradation of proteins by the N-end rule pathway in vivo. Moreover, this inhibition is shown to be selective for the two distinct classes of destabilizing amino-terminal residues in substrates of the N-end rule pathway.