Martins L J, Jensen L T, Simon J R, Keller G L, Winge D R
University of Utah Health Sciences Center, Salt Lake City, Utah 84132, USA.
J Biol Chem. 1998 Sep 11;273(37):23716-21. doi: 10.1074/jbc.273.37.23716.
The high affinity uptake systems for iron and copper ions in Saccharomyces cerevisiae involve metal-specific permeases and two known cell surface Cu(II) and Fe(III) metalloreductases, Fre1 and Fre2. Five novel genes found in the S. cerevisiae genome exhibit marked sequence similarity to Fre1 and Fre2, suggesting that the homologs are part of a family of proteins related to Fre1 and Fre2. The homologs are expressed genes in S. cerevisiae, and their expression is metalloregulated as is true with FRE1 and FRE2. Four of the homologs (FRE3-FRE6) are specifically iron-regulated through the Aft1 transcription factor. These genes are expressed either in cells limited for iron ion uptake by treatment with a chelator or in cells lacking the high affinity iron uptake system. Expression of FRE3-FRE6 is elevated in AFT1-1 cells and attenuated in aft1 null cells, showing that iron modulation occurs through the Aft1 transcriptional activator. The fifth homolog FRE7 is specifically copper-metalloregulated. FRE7 is expressed in cells limited in copper ion uptake by a Cu(I)-specific chelator or in cells lacking the high affinity Cu(I) permeases. The constitutive expression of FRE7 in MAC1 cells and the lack of expression in mac1-1 cells are consistent with Mac1 being the critical transcriptional activator of FRE7 expression. The 5' promoter sequence of FRE7 contains three copper-responsive promoter elements. Two elements are critical for Mac1-dependent FRE7 expression. Combinations of either the distal and central elements or the central and proximal elements result in copper-regulated FRE7 expression. Spacing between Mac1-responsive sites is important as shown by the attenuated expression of FRE7 and CTR1 when two elements are separated by over 100 base pairs. From the three Mac1-responsive elements in FRE7, a new consensus sequence for Mac1 binding can be established as TTTGC(T/G)C(A/G).
酿酒酵母中铁离子和铜离子的高亲和力摄取系统涉及金属特异性通透酶以及两种已知的细胞表面铜（II）和铁（III）金属还原酶Fre1和Fre2。在酿酒酵母基因组中发现的五个新基因与Fre1和Fre2具有显著的序列相似性，这表明这些同源物是与Fre1和Fre2相关的蛋白质家族的一部分。这些同源物是酿酒酵母中的表达基因，并且它们的表达如FRE1和FRE2一样受到金属调节。其中四个同源物（FRE3 - FRE6）通过Aft1转录因子受到铁的特异性调节。这些基因在通过螯合剂处理限制铁离子摄取的细胞中表达，或者在缺乏高亲和力铁摄取系统的细胞中表达。FRE3 - FRE6在AFT1 - 1细胞中的表达升高，而在aft1缺失细胞中减弱，表明铁调节是通过Aft1转录激活因子发生的。第五个同源物FRE7受到铜的特异性金属调节。FRE7在通过铜（I）特异性螯合剂限制铜离子摄取的细胞中表达，或者在缺乏高亲和力铜（I）通透酶的细胞中表达。FRE7在MAC1细胞中的组成型表达以及在mac1 - 1细胞中的不表达与Mac1是FRE7表达的关键转录激活因子一致。FRE7的5'启动子序列包含三个铜响应启动子元件。其中两个元件对于Mac1依赖性FRE7表达至关重要。远端和中央元件的组合或中央和近端元件的组合导致FRE7表达受到铜调节。当两个元件相隔超过100个碱基对时，FRE7和CTR1表达减弱，这表明Mac1响应位点之间的间距很重要。从FRE7中的三个Mac1响应元件可以确定Mac1结合的新共有序列为TTTGC(T/G)C(A/G)。
