Felice M Rosa, De Domenico Ivana, Li Liangtao, Ward Diane McVey, Bartok Beatrix, Musci Giovanni, Kaplan Jerry
Dipartimento di Scienze Microbiologiche Genetiche e Molecolari, Università di Messina, Salita Sperone 31, I-98166 Villaggio S. Agata, Messina I-98166, Italy.
J Biol Chem. 2005 Jun 10;280(23):22181-90. doi: 10.1074/jbc.M414663200. Epub 2005 Apr 7.
Saccharomyces cerevisiae transcriptionally regulates the expression of the plasma membrane high affinity iron transport system in response to iron need. This transport system is comprised of the products of the FET3 and FTR1 genes. We show that Fet3p and Ftr1p are post-translationally regulated by iron. Incubation of cells in high iron leads to the internalization and degradation of both Fet3p and Ftr1p. Yeast strains defective in endocytosis (Deltaend4) show a reduced iron-induced loss of Fet3p-Ftr1p. In cells with a deletion in the vacuolar protease PEP4, high iron medium leads to the accumulation of Fet3p and Ftr1p in the vacuole. Iron-induced degradation of Fet3p-Ftr1p is significantly reduced in strains containing a deletion of a gene, VTA1, which is involved in multivesicular body (MVB) sorting in yeast. Sorting through the MVB can involve ubiquitination. We demonstrate that Ftr1p is ubiquitinated, whereas Fet3p is not ubiquitinated. Iron-induced internalization and degradation of Fet3p-Ftr1p occurs in a mutant strain of the E3 ubiquitin ligase RSP5 (rsp5-1), suggesting that Rsp5p is not required. Internalization of Fet3p-Ftr1p is specific for iron and requires both an active Fet3p and Ftr1p, indicating that it is the transport of iron through the iron permease Ftr1p that is responsible for the internalization and degradation of the Fet3p-Ftr1p complex.
酿酒酵母会根据铁需求转录调控质膜高亲和力铁转运系统的表达。该转运系统由FET3和FTR1基因的产物组成。我们发现Fet3p和Ftr1p在翻译后受铁调控。将细胞置于高铁环境中孵育会导致Fet3p和Ftr1p的内化和降解。内吞作用缺陷的酵母菌株（Deltaend4）显示铁诱导的Fet3p - Ftr1p损失减少。在液泡蛋白酶PEP4缺失的细胞中，高铁培养基会导致Fet3p和Ftr1p在液泡中积累。在含有参与酵母多囊泡体（MVB）分选的基因VTA1缺失的菌株中，铁诱导的Fet3p - Ftr1p降解显著减少。通过MVB分选可能涉及泛素化。我们证明Ftr1p被泛素化，而Fet3p未被泛素化。铁诱导的Fet3p - Ftr1p内化和降解发生在E3泛素连接酶RSP5的突变菌株（rsp5 - 1）中，这表明不需要Rsp5p。Fet3p - Ftr1p的内化对铁具有特异性，并且需要活性的Fet3p和Ftr1p，这表明正是通过铁通透酶Ftr1p的铁转运导致了Fet3p - Ftr1p复合物的内化和降解。
