In vivo half-life of a protein is a function of its amino-terminal residue.
When a chimeric gene encoding a ubiquitin-beta-galactosidase fusion protein is expressed in the yeast Saccharomyces cerevisiae, ubiquitin is cleaved off the nascent fusion protein, yielding a deubiquitinated beta-galactosidase (beta gal). With one exception, this cleavage takes place regardless of the nature of the amino acid residue of beta gal at the ubiquitin-beta gal junction, thereby making it possible to expose different residues at the amino-termini of the otherwise identical beta gal proteins. The beta gal proteins thus designed have strikingly different half-lives in vivo, from more than 20 hours to less than 3 minutes, depending on the nature of the amino acid at the amino-terminus of beta gal. The set of individual amino acids can thus be ordered with respect to the half-lives that they confer on beta gal when present at its amino-terminus (the "N-end rule"). The currently known amino-terminal residues in long-lived, noncompartmentalized intracellular proteins from both prokaryotes and eukaryotes belong exclusively to the stabilizing class as predicted by the N-end rule. The function of the previously described posttranslational addition of single amino acids to protein amino-termini may also be accounted for by the N-end rule. Thus the recognition of an amino-terminal residue in a protein may mediate both the metabolic stability of the protein and the potential for regulation of its stability.
D000596:Amino Acids / Q000378:metabolism*; D004926:Escherichia coli; D006207:Half-Life; D008715:Methionine / Q000378:metabolism; D008954:Models, Biological; D011499:Protein Processing, Post-Translational; D011506:Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012441:Saccharomyces cerevisiae; D014452:Ubiquitins / Q000378:metabolism; D001616:beta-Galactosidase / Q000378:metabolism
D000596:Amino Acids; D011506:Proteins; D011994:Recombinant Proteins; D014452:Ubiquitins; D008715:Methionine; D001616:beta-Galactosidase