Ramanculov E, Young R
Department of Biochemistry and Biophysics, 2128 TAMU, Texas A&M University, 77843-2128, College Station, TX, USA.
Gene. 2001 Mar 7;265(1-2):25-36. doi: 10.1016/s0378-1119(01)00365-1.
The t protein of bacteriophage T4 shares with other holins the ability to cause the formation of a lethal membrane lesion which allows the phage endolysin to attack the peptidoglycan. Moreover, T, like other holins, acts in a saltatory manner at a precisely programmed time in the vegetative cycle. Unlike other holins, however, T has the unique ability to postpone its lethal function in response to a secondary infection by a T-even phage during the vegetative cycle. A signal transduction system that responds to the secondary infection is thought to be encoded by some of the numerous r genes, defined by mutations that abolish this lysis-inhibition (LIN) response. The primary structure of T differs from two main structural patterns found in more than 30 orthologous groups of holins. Genetic approaches were taken to probe the t sequence for features involved in membrane localization, functional timing and LIN regulation. Gene fusion analysis indicates that T has a single TMD near the N-terminus, with the bulk of the protein residing in the periplasm. Mapping and phenotypic analysis of deletion and point mutations in t indicates that the periplasmic domain of T is the major determinant of the timing mechanism and is involved in the LIN response.
噬菌体T4的t蛋白与其他孔蛋白一样，具有导致形成致死性膜损伤的能力，这种损伤使噬菌体溶菌酶能够攻击肽聚糖。此外，与其他孔蛋白一样，T在营养周期中精确编程的时间以跳跃方式起作用。然而，与其他孔蛋白不同的是，T具有独特的能力，在营养周期中响应T偶数噬菌体的二次感染而推迟其致死功能。一种响应二次感染的信号转导系统被认为由众多r基因中的一些编码，这些r基因由消除这种裂解抑制（LIN）反应的突变所定义。T的一级结构不同于在30多个孔蛋白直系同源组中发现的两种主要结构模式。采用遗传学方法探究t序列中与膜定位、功能时间和LIN调节相关的特征。基因融合分析表明，T在N端附近有一个单一的跨膜结构域，大部分蛋白质位于周质中。对t中的缺失和点突变进行定位和表型分析表明，T的周质结构域是时间机制的主要决定因素，并参与LIN反应。
