Johnson E S, Bartel B, Seufert W, Varshavsky A
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
EMBO J. 1992 Feb;11(2):497-505. doi: 10.1002/j.1460-2075.1992.tb05080.x.
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.
对于许多短寿命的真核生物蛋白质而言，与泛素结合形成多泛素链是降解前的必经步骤。结合的泛素部分作为降解的“二级”信号，因为其与底物蛋白的翻译后偶联是由底物的氨基酸序列介导的，这些氨基酸序列充当主要降解信号。我们报道融合蛋白泛素-脯氨酸-β-半乳糖苷酶（Ub-P-βgal）在酿酒酵母中寿命较短，因为其N端泛素部分充当自主的主要降解信号。该信号介导了与Ub-P-βgal中N端泛素的Lys48相连的多泛素链的形成。Ub-P-βgal的降解显示需要Ubc4，它是酿酒酵母中至少七种泛素结合酶之一。我们的发现提供了首个直接证据，证明单泛素部分可作为自主降解信号。这种普遍适用的顺式作用信号可用于操纵特定细胞内蛋白质在体内的半衰期。
