Ubiquitin as a degradation signal.
For many short-lived eukaryotic proteins, conjugation to ubiquitin, yielding a multiubiquitin chain, is an obligatory pre-degradation step. The conjugated ubiquitin moieties function as a 'secondary' signal for degradation, in that their posttranslational coupling to a substrate protein is mediated by amino acid sequences of the substrate that act as a primary degradation signal. We report that the fusion protein ubiquitin--proline--beta-galactosidase (Ub-P-beta gal) is short-lived in the yeast Saccharomyces cerevisiae because its N-terminal ubiquitin moiety functions as an autonomous, primary degradation signal. This signal mediates the formation of a multiubiquitin chain linked to Lys48 of the N-terminal ubiquitin in Ub-P-beta gal. The degradation of Ub-P-beta gal is shown to require Ubc4, one of at least seven ubiquitin-conjugating enzymes in S.cerevisiae. Our findings provide the first direct evidence that a monoubiquitin moiety can function as an autonomous degradation signal. This generally applicable, cis-acting signal can be used to manipulate the in vivo half-lives of specific intracellular proteins.
Johnson
E S
ES
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Bartel
B
B
Seufert
W
W
Varshavsky
A
A
D000595:Amino Acid Sequence; D001483:Base Sequence; D007700:Kinetics; D008969:Molecular Sequence Data; D016254:Mutagenesis, Insertional; D009838:Oligodeoxyribonucleotides; D010957:Plasmids; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015183:Restriction Mapping; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism*; D015398:Signal Transduction; D014452:Ubiquitins / Q000235:genetics / Q000378:metabolism*; D001616:beta-Galactosidase / Q000235:genetics / Q000378:metabolism
D009838:Oligodeoxyribonucleotides; D011993:Recombinant Fusion Proteins; D014452:Ubiquitins; D001616:beta-Galactosidase