Montag D, Riede I, Eschbach M L, Degen M, Henning U
Max-Planck-Institut für Biologie, Tübingen, F.R.G.
J Mol Biol. 1987 Jul 5;196(1):165-74. doi: 10.1016/0022-2836(87)90519-5.
Proteins 38 of bacteriophages T2, K3, Ox2 and M1 are located at the free ends of their long tail fibers and function as adhesins, i.e. they mediate binding to the bacterial receptors. The latter three phages use the Escherichia coli outer membrane protein OmpA as a receptor, while T2 uses the outer membrane proteins OmpF or Ttr. The DNA sequences of genes 38 of phages Ox2 and M1 have been determined and are compared with those known for T2 and K3. The genes encode 262(T2), 260(K3), 266(Ox2) and 262(M1) amino acid residues. Three domains are distinguishable in these proteins. There are two conserved regions encompassing about 120 NH2-terminal and about 25 CO2H-terminal residues, respectively. The area between these was found to be hypervariable, and it is shown that a very large number of amino acid substitutions, deletions and/or insertions have occurred. Glycine-rich stretches are present within and flanking these areas. Their positions are essentially conserved, indicating an important structural role in receptor recognition. The hypervariability, most likely caused by a constant struggle with bacterial phage-resistant mutants, is so drastic that one cannot discern that T2 uses different receptors from those of the other phages. The partially known sequence of gene 38 of phage T4 has been completed. The gene encodes a protein consisting of 183 amino acid residues. The amino acid composition and sequence of this protein is completely different from those of phages T2, K3, Ox2 and M1. Also, the protein is functionally unrelated to the other proteins 38: it is not present in phage T4 and, unlike the other proteins 38, is required for the efficient dimerization of protein 37. All phages under study are of the same morphology and the genomic organization of the tail fiber genes is identical, with genes 36, 37 and 38 most likely representing, in this order, a transcriptional unit. Sequence similarities between the CO2H-termini of genes 37 of the non-T4 phages and gene 38 of phage T4 were found; this part of gene 37 does not exist in T4. It is suggested that gene 38 of phage T4 originated from a segment of gene 37 of a T2-type phage. Gene 38 of phage T4 is not unique, DNA-DNA hybridization experiments indicated that two other T-even type phages, TuIa and TuIb, possess a T4-type gene 38.
噬菌体T2、K3、Ox2和M1的蛋白质38位于其长尾丝的自由末端，起粘附素的作用，即介导与细菌受体的结合。后三种噬菌体利用大肠杆菌外膜蛋白OmpA作为受体，而T2利用外膜蛋白OmpF或Ttr。已经确定了噬菌体Ox2和M1的基因38的DNA序列，并与已知的T2和K3的序列进行了比较。这些基因分别编码262个（T2）、260个（K3）、266个（Ox2）和262个（M1）氨基酸残基。在这些蛋白质中可区分出三个结构域。有两个保守区域，分别包含约120个氨基末端和约25个羧基末端残基。发现这两个区域之间的区域高度可变，并且已表明发生了大量的氨基酸替换、缺失和/或插入。富含甘氨酸的片段存在于这些区域内及其侧翼。它们的位置基本保守，表明在受体识别中起重要的结构作用。这种高度变异性很可能是由于与细菌噬菌体抗性突变体的持续斗争所致，其程度非常剧烈，以至于无法辨别T2与其他噬菌体使用不同的受体。噬菌体T4的基因38的部分已知序列已完成。该基因编码一种由183个氨基酸残基组成的蛋白质。该蛋白质的氨基酸组成和序列与噬菌体T2、K3、Ox2和M1完全不同。此外，该蛋白质在功能上与其他蛋白质38无关：它不存在于噬菌体T4中，并且与其他蛋白质38不同，它是蛋白质37有效二聚化所必需的。所有研究的噬菌体具有相同的形态，尾丝基因的基因组组织相同，基因36、37和38很可能按此顺序代表一个转录单位。发现非T4噬菌体的基因37的羧基末端与噬菌体T4的基因38之间存在序列相似性；基因37的这一部分在T4中不存在。有人提出，噬菌体T4的基因38起源于T2型噬菌体的基因37的一段。噬菌体T4的基因38并非独一无二，DNA-DNA杂交实验表明，另外两种T偶数型噬菌体TuIa和TuIb拥有T4型基因38。
