CRYSTAL-STRUCTURE OF LAC REPRESSOR CORE TETRAMER AND ITS IMPLICATIONS FOR DNA LOOPING
CRYSTAL-STRUCTURE OF LAC REPRESSOR CORE TETRAMER AND ITS IMPLICATIONS FOR DNA LOOPING
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DOI：
10.1126/science.7792597
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发表时间：
1995-06-23
期刊：
影响因子：
56.9
通讯作者：
STEITZ, TA
中科院分区：
文献类型：
--
作者：
FRIEDMAN, AM;FISCHMANN, TO;STEITZ, TA
在2.6埃分辨率下测定了与诱导剂异丙基-β-D-硫代半乳糖苷复合的大肠杆菌乳糖阻遏物（LacR）的胰蛋白酶核心片段的晶体结构。四元结构由两个二价对称的二聚体组成，它们几乎彼此平行。这种结构将完整LacR的所有四个DNA结合结构域置于四聚体的同一侧，并导致两个二聚体之间的深V形裂缝。每个单体贡献一个羧基末端螺旋的反平行四螺旋束，作为一个四聚化结构域的功能。一些突变减少DNA结合的侧链在氨基末端附近的表面上形成簇。将与先前通过核磁共振确定的算子复合的DNA结合结构域的结构放置在该表面上导致两个算子彼此相邻且几乎平行。结构上的考虑表明，两个二聚体的LacR可以灵活地改变它们的相对方向，以结合到已知的两个运营商之间的不同间距。
The crystal structure of the tryptic core fragment of the lac repressor of Escherichia coli (LacR) complexed with the inducer isopropyl-beta-D-thiogalactoside was determined at 2.6 Angstrom resolution. The quaternary structure consists of two dyad-symmetric dimers that are nearly parallel to each other. This structure places all four DNA binding domains of intact LacR on the same side of the tetramer, and results in a deep, V-shaped cleft between the two dimers. Each monomer contributes a carboxyl-terminal helix to an antiparallel four-helix bundle that functions as a tetramerization domain. Some of the side chains whose mutation reduce DNA binding form clusters on a surface near the amino terminus. Placing the structure of the DNA binding domain complexed with operator previously determined by nuclear magnetic resonance onto this surface results in two operators being adjacent and nearly parallel to each other. Structural considerations suggest that the two dimers of LacR may flexibly alter their relative orientation in order to bind to the known varied spacings between two operators.