二聚体
结晶学
蛋白质亚单位
DNA
螺旋(腹足类)
噬菌体
核苷酸
DNA复制
生物物理学
透射电子显微镜
分子
化学
病毒蛋白
生物
大肠杆菌
病毒
材料科学
生物化学
纳米技术
病毒学
有机化学
基因
蜗牛
生态学
作者
G.G. Kneale,Richard B. Freeman,D.A. Marvin
标识
DOI:10.1016/0022-2836(82)90329-1
摘要
X-ray fibre diffraction and scanning transmission electron microscopy have been used to investigate the structure of an intracellular complex between circular single-stranded viral DNA and a viral DNA-binding protein. This complex is an intermediate between replication and assembly of the filamentous bacteriophage Pf1. By scanning transmission electron microscopy, the complex has a length of 1.00 μm and Mr = 29.6 × 106. It consists of 1770 protein subunits, each of 15,400 Mr, and one viral DNA molecule of 2.3 × 106Mr: there are 4.2 ± 0.5 nucleotides per subunit. The structure is flexible in solution, but in oriented dry fibres it forms a regular helix of 45 Å pitch having 6.0 dimeric protein subunits per turn, with an axial spacing of 7.5 Å between dimers and 1.9 Å between adjacent nucleotides. Model calculations suggest that the protein dimers may be oriented in a direction approximately perpendicular to the 45 Å helix, so that each dimer spans the two anti-parallel DNA chains. The results imply that conformational changes are required of the DNA as it is transferred from the double-stranded form to the replication-assembly complex, and subsequently to the virion.
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