Beck T, Schmidt A, Hall M N
Department of Biochemistry, Biozentrum, University of Basel, CH-4056 Basel, Switzerland.
J Cell Biol. 1999 Sep 20;146(6):1227-38. doi: 10.1083/jcb.146.6.1227.
In Saccharomyces cerevisiae, amino acid permeases are divided into two classes. One class, represented by the general amino acid permease GAP1, contains permeases regulated in response to the nitrogen source. The other class, including the high affinity tryptophan permease, TAT2, consists of the so-called constitutive permeases. We show that TAT2 is regulated at the level of protein stability. In exponentially growing cells, TAT2 is in the plasma membrane and also accumulates in internal compartments of the secretory pathway. Upon nutrient deprivation or rapamycin treatment, TAT2 is transported to and degraded in the vacuole. The ubiquitination machinery and lysine residues within the NH(2)-terminal 31 amino acids of TAT2 mediate ubiquitination and degradation of the permease. Starvation-induced degradation of internal TAT2 is blocked in sec18, sec23, pep12, and vps27 mutants, but not in sec4, end4, and apg1 mutants, suggesting that, upon nutrient limitation, internal TAT2 is diverted from the late secretory pathway to the vacuolar pathway. Furthermore, our results suggest that TAT2 stability and sorting are controlled by the TOR signaling pathway, and regulated inversely to that of GAP1.
在酿酒酵母中,氨基酸通透酶分为两类。一类以通用氨基酸通透酶GAP1为代表,包含响应氮源而受到调控的通透酶。另一类包括高亲和力色氨酸通透酶TAT2,由所谓的组成型通透酶组成。我们发现TAT2在蛋白质稳定性水平上受到调控。在指数生长的细胞中,TAT2存在于质膜中,也在分泌途径的内部区室中积累。在营养剥夺或雷帕霉素处理后,TAT2被转运至液泡并在其中降解。泛素化机制以及TAT2氨基末端31个氨基酸内的赖氨酸残基介导了该通透酶的泛素化和降解。饥饿诱导的内部TAT2降解在sec18、sec23、pep12和vps27突变体中被阻断,但在sec4、end4和apg1突变体中未被阻断,这表明在营养限制时,内部TAT2从晚期分泌途径转向液泡途径。此外,我们的结果表明TAT2的稳定性和分选受TOR信号通路控制,且与GAP1的调控相反。