Zhang L, Bermingham-McDonogh O, Turcotte B, Guarente L
Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
Proc Natl Acad Sci U S A. 1993 Apr 1;90(7):2851-5. doi: 10.1073/pnas.90.7.2851.
The yeast transcriptional activator HAP1 contains a DNA-binding domain homologous to the zinc finger of GAL4 and an adjacent regulatory domain that blocks DNA binding in the absence of the inducer heme. We show that short HAP1 fragments containing the zinc finger are unable to bind to DNA but can be rescued by antibody to the HAP1 zinc finger. These fragments are missing a coiled-coil sequence similar to that within the dimerization domain of GAL4 and dimerization domains of myosin heavy chain. We surmise that the antibody promotes DNA binding by bringing together two monomers. Interestingly, the antibody will also promote DNA binding of a larger HAP1 fragment containing the DNA-binding and the heme-regulatory domains. This suggests that the regulatory domain acts by preventing dimerization of HAP1 in the absence of heme. Consistent with this view is an in vivo assay that also reveals that heme promotes HAP1 dimerization in yeast cells.
酵母转录激活因子HAP1含有一个与GAL4锌指同源的DNA结合结构域以及一个相邻的调控结构域，该调控结构域在缺乏诱导物血红素时会阻断DNA结合。我们发现，含有锌指的短HAP1片段无法与DNA结合，但可被针对HAP1锌指的抗体拯救。这些片段缺失了一段与GAL4二聚化结构域及肌球蛋白重链二聚化结构域内序列相似的卷曲螺旋序列。我们推测，抗体通过使两个单体聚集在一起促进DNA结合。有趣的是，该抗体还会促进含有DNA结合结构域和血红素调控结构域的较大HAP1片段与DNA的结合。这表明调控结构域在缺乏血红素时通过阻止HAP1二聚化发挥作用。与此观点一致的是一项体内试验，该试验也表明血红素可促进酵母细胞中HAP1的二聚化。
