Mechanisms of Size- and Shape-Determination in Supramolecular Structures by Genetic Information

本研究以λ噬菌体为材料，对超分子结构的大小和形状决定机制进行了研究。以往的研究表明，主要衣壳蛋白GPE可以组装成五类不同大小和形状的结构，这取决于它所包含的错义突变。在本研究中，我通过对DNA碱基序列中各种突变的分配，阐明了GPE的结构与功能的关系，为解释GPE的决定机制奠定了物质基础。作为具体结果，已经完全确定了琥珀突变的43个位点的位置。此外，我已经对31个错义突变体中的28个进行了测序，这些错义突变体产生了不同大小和形状的头部相关结构。在后者的突变体中，有许多是Ser、Pro或Gly的替换，这表明GPE的功能位点富含位于分子表面的-lt；beta&gt；-转角。我们先前的工作表明，尾巴的长度由“统治蛋白”GPH的长度决定。在本研究中，通过体外遗传操作，获得了30个该基因中部大小不等的突变体。其中12个被发现产生短尾的噬菌体颗粒，这表明在大多数情况下，只要缺失在框内，尾巴组装就会进行。在这12个噬菌体颗粒中，有两个有脆弱的尾尖，其余十个在DNA注射过程中存在缺陷。因此，GPH的中部似乎在这些功能中起着重要的作用，而在尾部组装中则是必不可少的。由于尾管的长度与GPH的氨基酸残基数量大致成正比，GPH的整个分子似乎起到了测量尾部长度的尺子的作用。

This study was performed to elucidate the mechanisms of size- and shape-determination in supramolecular structures by using lambda phage as the material.My previous studies have shown that the major capsid protein gpE can assemble into five classes of structures having various size and shape, depending on the missense mutation it contains. In this study I have clarified the structure-function relationship of gpE and established a material basis for the explanation of the determination mechanisms, through assignment of various mutations in the DNA base sequence. As concrete results, the positions of amber mutations at 43 sites have been determined completely. Moreover, I have sequenced 28 of the 31 missense mutants which produce head-related structures of various size and shape. Among the latter mutants many are substitutions of Ser, Pro or Gly, which suggests that the functional sites of gpE are rich in <beta> -turns located on the surface of the molecule.Our previous work has indicated that the tail length is determined by the length of the "ruler protein" gpH. In this study thirty mutants having deletions of various size in the middle part of this gene were made by in vitro genetic manipulation. Twelve of them were found to produce phage particles with short tails, which shows that tail assembly proceeds in most cases as long as the deletions are in-frame. Of these twelve phage particles two have fragile tail tips, whereas the rest ten are defective in DNA injection. Therefore, the middle part of gpH seems to play an important role in these functions, while it is dispensable in tail assembly. Since the length of the tail tube is roughly proportional to the number of amino acid residues of gpH, the whole molecule of gpH seems to function as a ruler to measure the tail length.