Witkiewicz H, Schweiger M
J Theor Biol. 1985 Oct 21;116(4):587-605. doi: 10.1016/s0022-5193(85)80089-8.
The icosahedral shape of the lambda head suggests a 12-subunit structure of the collapsed DNA inside. The internal space of an icosahedron can optimally be filled by 12 geometrical figures each of which is a combination of a cone and more than half of a sphere. Such a pear-like geometrical figure is, in fact, formed spontaneously by DNA collapsed under certain conditions in vitro (Eickbush & Moudrianakis, 1978). It is proposed that a pear-like structure formed by about 4000 bp is the fundamental structural subunit of packaged lambda DNA. A possible arrangement of the 12 subunits inside the phage head relative to the tail is discussed. We hypothesize that lambda DNA is packaged into proheads in its condensed form. A driving force promoting the DNA translocation could be an ATP-dependent activity of a DNA topoisomerase (gpA/gpNu1), which would induce further reduction in the linking number of the already strongly negatively supercoiled DNA by rotation of one DNA strand around the other. The additional strain accumulated at the end of DNA molecule bound by the topoisomerase beyond a critical value would lead to regional collapse of the viral genome into a pear-like structure.
λ噬菌体头部的二十面体形状表明其内部折叠的DNA具有12亚基结构。二十面体的内部空间可以由12个几何图形最佳填充，每个几何图形都是一个圆锥体和超过半个球体的组合。事实上，这种梨形几何图形是由体外特定条件下折叠的DNA自发形成的（艾克布什和穆德里亚纳基斯，1978年）。有人提出，由约4000个碱基对形成的梨形结构是包装的λ噬菌体DNA的基本结构亚基。讨论了噬菌体头部内12个亚基相对于尾部的可能排列方式。我们假设λ噬菌体DNA以浓缩形式包装进原头部。促进DNA易位的驱动力可能是DNA拓扑异构酶（gpA/gpNu1）的ATP依赖性活性，它会通过一条DNA链围绕另一条链的旋转，导致已经高度负超螺旋的DNA的连环数进一步减少。在拓扑异构酶结合的DNA分子末端积累的额外张力超过临界值时，将导致病毒基因组区域折叠成梨形结构。
