Takeda S, Hoshida K, Arisaka F
Department of Life Science, Faculty of Bioscience and Biotechnology, Tokyo Institute of Technology, Yokohama, Japan.
Biochim Biophys Acta. 1998 May 19;1384(2):243-52. doi: 10.1016/s0167-4838(98)00016-8.
Tail lysozyme of bacteriophage T4, product of gene 5 (gp5), functions upon infection by locally digging a hole in the peptidoglycan layer, so that the tail tube, through which the phage DNA is injected, can penetrate to the inner membrane. It has been inferred from DNA sequence and expression of the tail lysozyme on a plasmid in Escherichia coli that the tail lysozyme is synthesized as a precursor of 62 K and is later cleaved to form a mature tail lysozyme of 42 K. Furthermore, gp5 has a region that is highly homologous to T4 lysozyme, gpe, that is the product of gene e and functions for 'lysis from within'. As an approach to elucidation of structure-function relationship of gp5, we determined mutational sites of gene 5 mutants that have heat sensitive virions, are temperature sensitive for growth, or require an amber suppressor. All the mutational sites were mapped in the region corresponding to the mature tail lysozyme. Among the ts mutants, 5ts1 was a pseudo-revertant of an amber mutant which bypasses gene e. It was mapped in the region which had a high homology to gpe, which is well known as T4 lysozyme. The other mutational sites will be also discussed in relation to the phenotypes of the mutants.
噬菌体T4的尾部溶菌酶是基因5（gp5）的产物，在感染时通过在肽聚糖层上局部打孔发挥作用，使注入噬菌体DNA的尾管能够穿透到内膜。从DNA序列以及在大肠杆菌质粒上表达的尾部溶菌酶推断，尾部溶菌酶最初合成时是一个62K的前体，随后被切割形成一个42K的成熟尾部溶菌酶。此外，gp5有一个区域与T4溶菌酶（gpe，基因e的产物，具有“自内裂解”功能）高度同源。作为阐明gp5结构与功能关系的一种方法，我们确定了具有热敏感病毒体、生长温度敏感或需要琥珀抑制子的基因5突变体的突变位点。所有突变位点都定位在对应于成熟尾部溶菌酶的区域。在温度敏感突变体中，5ts1是一个绕过基因e的琥珀突变体的假回复体。它定位在与gpe高度同源的区域，gpe即众所周知的T4溶菌酶。其他突变位点也将结合突变体的表型进行讨论。
