Grzeskowiak K, Goodsell D S, Kaczor-Grzeskowiak M, Cascio D, Dickerson R E
Department of Chemistry and Biochemistry, University of California, Los Angeles 90024.
Biochemistry. 1993 Aug 31;32(34):8923-31. doi: 10.1021/bi00085a025.
Stacked B-DNA double helices of sequence C-C-A-A-G-C-T-T-G-G exhibit the same 23 degrees bend at -T-G-G C-C-A- across the nonbonded junction between helices that is observed in the middle of the decamer helix of sequence C-A-T-G-G-C-C-A-T-G, even though the space group (hexagonal vs orthorhombic), crystal packing, and connectedness at the center of the bent segment are quite different. An identical bend occurs across the interhelix junction of every monoclinic crystal structure of sequence C-C-A-x-x-x-x-T-G-G, suggesting that T-G-G-C-C-A constitutes a natural bending element in B-DNA. The bend occurs by rolling stacked base pairs about their long axes; there is no "tilt" component. Of the three possible models for A-tract bending--bent-A-tract, junction bends, or bent-non-A--which cannot be distinguished by solution measurements, all crystallographic evidence over the past 10 years unanimously supports the non-A regions as the actual bending loci.
序列为C-C-A-A-G-C-T-T-G-G的堆积B-DNA双螺旋在-T-G-G C-C-A-处沿着螺旋之间的非键合连接点呈现出23度的弯曲，这与在序列为C-A-T-G-G-C-C-A-T-G的十聚体螺旋中间观察到的弯曲相同，尽管空间群（六方晶系与正交晶系）、晶体堆积以及弯曲片段中心的连接性有很大不同。在序列为C-C-A-x-x-x-x-T-G-G的每个单斜晶体结构的螺旋间连接点处都出现了相同的弯曲，这表明T-G-G-C-C-A构成了B-DNA中的一个天然弯曲元件。这种弯曲是通过堆叠的碱基对绕其长轴滚动产生的；不存在“倾斜”分量。在过去10年中，所有晶体学证据都一致支持非A区域作为实际的弯曲位点，而通过溶液测量无法区分的A-序列弯曲的三种可能模型——弯曲的A-序列、连接点弯曲或弯曲的非A序列。
