The yeast heme-responsive transcriptional activator Hap1 is a preexisting dimer in the absence of heme
The yeast heme-responsive transcriptional activator Hap1 is a preexisting dimer in the absence of heme
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DOI：
10.1074/jbc.274.32.22770
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发表时间：
1999-08-06
影响因子：
4.8
通讯作者：
Zhang, L
中科院分区：
文献类型：
--
作者：
Hon, T;Hach, A;Zhang, L
在没有血红素的情况下，Hap1与分子伴侣如Hsp90和Ydj1结合，形成称为HMC的高级复合物。血红素破坏这种复合物，并允许Hap1以高亲和力结合DNA，从而激活转录。血红素对Hap1活性的调节类似于类固醇对类固醇受体的调节，这涉及分子伴侣。类固醇受体在没有配体的情况下与分子伴侣结合时通常以单体形式存在，但在被类固醇激活时以二聚体形式存在。此外，以前的研究表明，二聚化可能是重要的血红素激活Hap1。因此，我们确定是否Hap1是一个单体或低聚物在血红素的情况下。通过共洗脱两个Hap1大小的变体，并通过比较DNA结合特性的HMC和Hap1二聚体，我们表明，Hap1是一个预先存在的二聚体中的HMC。此外，增加Hap1的过表达引起Hap1 DNA结合和转录活性的进行性增加。我们的数据表明，在血红素的情况下，Hap1作为二聚体存在，并且两个亚基在DNA结合中协同作用。Hap1抑制至少部分是由抑制预先存在的二聚体的DNA结合活性引起的。
In the absence of heme, Hap1 is associated with molecular chaperones such as Hsp90 and Ydj1 and forms a higher order complex termed HMC. Heme disrupts this complex and permits Hap1 to bind to DNA with high affinity, thereby activating transcription, Heme regulation of Hap1 activity is analogous to the regulation of steroid receptors by steroids, which involves molecular chaperones. Steroid receptors often exist as monomers when associated with molecular chaperones in the absence of ligand but as dimers when activated by steroids. Furthermore, previous studies indicate that dimerization might be important for heme activation of Hap1. We therefore determined whether Hap1 is a monomer or oligomer in the absence of heme. By coeluting two Hap1 size variants and by comparing DNA binding properties of the HMC and Hap1 dimer, we show that Hap1 is a preexisting dimer in the HMC. Further, increasing overexpression of Hap1 caused progressive increases in Hap1 DNA binding and transcriptional activities. Our data suggest that in the absence of heme, Hap1 exists as a dimer, and the two subunits act cooperatively in DNA binding. Hap1 repression is caused, at least in part, by inhibition of the DNA binding activity of the preexisting dimer.