Mori K, Ogawa N, Kawahara T, Yanagi H, Yura T
HSP Research Institute, Kyoto Research Park, Shimogyo-ku, Kyoto 600-8813, Japan.
J Biol Chem. 1998 Apr 17;273(16):9912-20. doi: 10.1074/jbc.273.16.9912.
When unfolded proteins are accumulated in the endoplasmic reticulum (ER), an intracellular signaling pathway termed the unfolded protein response (UPR) is activated to induce transcription of ER-localized molecular chaperones and folding enzymes in the nucleus. In Saccharomyces cerevisiae, at least six lumenal proteins including essential Kar2p and Pdi1p are known to be regulated by the UPR. We and others recently demonstrated that the basic-leucine zipper protein Hac1p/Ern4p functions as a trans-acting factor responsible for the UPR. Hac1p binds directly to the cis-acting unfolded protein response element (UPRE) responsible for Kar2p induction. Moreover, we showed that the KAR2 UPRE contains an E box-like palindrome separated by one nucleotide (CAGCGTG) that is essential for its function. We report here that the promoter regions of each of five target proteins (Kar2p, Pdi1p, Eug1p, Fkb2p, and Lhs1p) contain a single UPRE sequence that is necessary and sufficient for induction and that binds specifically to Hac1p in vitro. All of the five functional UPRE sequences identified contain a palindromic sequence that has, in four cases, a spacer of one C nucleotide. This unique characteristic of UPRE explains why only a specific set of proteins are induced in the UPR to cope with ER stress.
当未折叠蛋白在内质网（ER）中积累时，一种称为未折叠蛋白反应（UPR）的细胞内信号通路被激活，以诱导细胞核中内质网定位的分子伴侣和折叠酶的转录。在酿酒酵母中，已知至少六种腔内蛋白（包括必需的Kar2p和Pdi1p）受UPR调控。我们和其他人最近证明，碱性亮氨酸拉链蛋白Hac1p/Ern4p作为负责UPR的反式作用因子发挥作用。Hac1p直接结合负责Kar2p诱导的顺式作用未折叠蛋白反应元件（UPRE）。此外，我们表明，KAR2 UPRE包含一个由一个核苷酸（CAGCGTG）隔开的类似E盒的回文序列，这对其功能至关重要。我们在此报告，五个靶蛋白（Kar2p、Pdi1p、Eug1p、Fkb2p和Lhs1p）中每一个的启动子区域都包含一个单一的UPRE序列，该序列对于诱导是必要且充分的，并且在体外与Hac1p特异性结合。鉴定出的所有五个功能性UPRE序列都包含一个回文序列，在四种情况下，该回文序列有一个C核苷酸的间隔。UPRE的这一独特特征解释了为什么在UPR中只诱导一组特定的蛋白来应对内质网应激。
