Allen M J, Tench R J, Mazrimas J A, Balooch M, Siekhaus W J, Balhorn R
Biomedical Sciences Division, Lawrence Livermore National Laboratory, Livermore, CA 94550.
Scanning Microsc. 1993 Jun;7(2):563-74; discussion 574-6.
Three duplex DNAs 22, 47, and 100 base-pairs in length have been imaged with the scanning tunneling microscope (STM) after deposition on highly oriented pyrolytic graphite (HOPG). Images of the 47 base-pair (bp) molecules are resolved sufficiently to identify the two phosphodiester strands, the direction of helical coiling (this molecule contains three turns of left-handed helix), and single-stranded ends. Length measurements indicate that all three DNA sequences have adopted an "A-like" conformation. DNA-protamine complexes were also prepared and imaged under similar conditions. Length measurements of the complexes demonstrate that the binding of bull protamine 1 to the 47-mer stabilizes the DNA in a B conformation and prevents the B to A transition that has been shown to occur as the DNA molecules dehydrate on the surface. Measurements of the diameter of the complex (3 nm) were also obtained and were found to be only slightly larger than the DNA molecule. This observation is consistent with the binding of the protamine molecule inside one of the grooves.
三种长度分别为22、47和100个碱基对的双链DNA在沉积于高度定向热解石墨（HOPG）上后，已用扫描隧道显微镜（STM）成像。47个碱基对（bp）分子的图像分辨率足够高，能够识别两条磷酸二酯链、螺旋盘绕方向（该分子包含三圈左手螺旋）以及单链末端。长度测量表明，所有三种DNA序列均采用了“类A”构象。还制备了DNA-鱼精蛋白复合物，并在类似条件下成像。复合物的长度测量表明，牛鱼精蛋白1与47聚体的结合使DNA稳定在B构象，并防止了随着DNA分子在表面脱水而发生的B到A的转变。还获得了复合物直径（3纳米）的测量值，发现其仅略大于DNA分子。这一观察结果与鱼精蛋白分子在其中一个凹槽内的结合情况一致。
