Sauer R T, Smith D L, Johnson A D
Department of Microbiology, University of California, San Francisco 94143.
Genes Dev. 1988 Jul;2(7):807-16. doi: 10.1101/gad.2.7.807.
The yeast alpha 2 protein, the product of the MAT alpha 2 gene, is a regulator of yeast cell type; it turns off transcription of the a-specific genes by binding to an operator located upstream of each gene. In this paper we describe the domain structure, subunit organization, and some unusual features of the way this protein contacts its operator. We show that the protein is folded into two domains. The carboxy-terminal domain binds specifically to the operator; the amino-terminal domain contains dimerization contacts. The alpha 2 dimer differs from those of the phage repressors in that it is flexible and therefore is able to bind tightly to differently spaced operator half-sites. In the natural operator, the centers of the operator half-sites are two and one-half turns of DNA apart, exposing them on opposite sides of the DNA helix. We show that the design of alpha 2 allows a dimer to reach across its operator such that it occupies the two half-sites but leaves the middle of the operator available to other proteins.
酵母α2蛋白是MATα2基因的产物，是酵母细胞类型的调节因子；它通过与每个基因上游的操纵子结合来关闭a特异性基因的转录。在本文中，我们描述了该蛋白的结构域结构、亚基组织以及该蛋白与操纵子结合方式的一些不寻常特征。我们表明该蛋白折叠成两个结构域。羧基末端结构域特异性地与操纵子结合；氨基末端结构域包含二聚化接触位点。α2二聚体与噬菌体阻遏物的二聚体不同，它具有灵活性，因此能够紧密结合到间隔不同的操纵子半位点上。在天然操纵子中，操纵子半位点的中心相隔两个半圈的DNA，使它们暴露在DNA螺旋的相对两侧。我们表明，α2的设计允许一个二聚体跨越其操纵子，使其占据两个半位点，但让操纵子的中间部分可供其他蛋白质使用。
