Kozloff L M, Verses C, Lute M, Crosby L K
J Virol. 1970 Jun;5(6):740-53. doi: 10.1128/JVI.5.6.740-753.1970.
The protein component of the T-even bacteriophage coat which binds the phage-specific dihydropteroyl polyglutamate has been identified as the phage-induced dihydrofolate reductase. Dihydrofolate reductase activity has been found in highly purified preparations of T-even phage ghosts and phage substructures after partial denaturation. The highest specific enzymatic activity was found in purified tail plate preparations, and it was concluded that this enzyme was a structural component of the phage tail plate. Phage viability was directly correlated with the enzymological properties of the phage tail plate dihydrofolate reductase. All reactions catalyzed by this enzyme which changed the oxidation state of the phage dihydrofolate also inactivated the phage. Properties of two T4D dihydrofolate reductase-negative mutants, wh1 and wh11, have been examined. Various lines of evidence support the view that the product of the wh locus of the phage genome is normally incorporated into the phage tail structure. The effects of various dihydrofolate reductase inhibitors on phage assembly in in vitro complementation experiments with various extracts of conditional lethal T4D mutants have been examined. These inhibitors were found to specifically block complementation when added to extracts which did not contain preformed tail plates. If tail plates were present, inhibitors such as aminopterin, did not affect further phage assembly. This specific inhibition of tail plate formation in vitro confirms the analytical and genetic evidence that this phage-induced "early" enzyme is a component of the phage coat.
与噬菌体特异性二氢蝶酰多聚谷氨酸结合的T偶数噬菌体外壳蛋白成分已被鉴定为噬菌体诱导的二氢叶酸还原酶。在部分变性后的T偶数噬菌体空壳和噬菌体亚结构的高度纯化制剂中发现了二氢叶酸还原酶活性。在纯化的尾板制剂中发现了最高的比酶活性，由此得出结论，该酶是噬菌体尾板的结构成分。噬菌体活力与噬菌体尾板二氢叶酸还原酶的酶学性质直接相关。该酶催化的所有改变噬菌体二氢叶酸氧化态的反应也会使噬菌体失活。已检测了两个T4D二氢叶酸还原酶阴性突变体wh1和wh11的特性。各种证据支持这样一种观点，即噬菌体基因组wh位点的产物通常会整合到噬菌体尾部结构中。已检测了各种二氢叶酸还原酶抑制剂在与条件致死性T4D突变体的各种提取物进行的体外互补实验中对噬菌体组装的影响。当将这些抑制剂添加到不含预先形成的尾板的提取物中时，发现它们会特异性地阻断互补作用。如果存在尾板，诸如氨甲蝶呤之类的抑制剂不会影响进一步的噬菌体组装。体外对尾板形成的这种特异性抑制证实了分析和遗传学证据，即这种噬菌体诱导的“早期”酶是噬菌体外壳的一个成分。
