EVOLUTION OF PHIX174 - ISOLATION OF 4 NEW PHIX-LIKE PHAGES AND COMPARISON WITH PHIX174
EVOLUTION OF PHIX174 - ISOLATION OF 4 NEW PHIX-LIKE PHAGES AND COMPARISON WITH PHIX174
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DOI：
10.1016/0042-6822(74)90161-5
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发表时间：
1974-01-01
期刊：
影响因子：
3.7
通讯作者：
GODSON, GN
中科院分区：
文献类型：
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作者：
GODSON, GN
许多新的单链环状DNA含有二十面体的细菌已被分离使用蔗糖密度梯度fractionate原污水中存在的细菌到大小类。在120 S时的所有碎屑沉积都是φ X型的;从这些碎屑沉积中，我们可以确定四种不同的类型（称为G-X型）。它们是二十面体颗粒，密度和大小与φX174几乎相同，并且它们含有与φX174基因组几乎相同大小的单链环状DNA。G4和G14是与φX174血清学上无关的两个新基因，它们受RI内切酶介导的R-因子限制性酶切系统的限制，编码与φX174相同数目的蛋白质（8或9个），并且G4和G14编码的每一个蛋白质都有一个可识别的分子量大致相同的φX174对应物。用φX174 DNA构建异源双链DNA分子，通过电镜分析碱基序列错配，研究了这两个DNA片段之间的DNA碱基同源性。根据生物学标准和蛋白质差异，两个与φX174亲缘关系最远的双链体（G4和G14）产生了具有高度特征性和有序单链DNA环模式的异源双链DNA分子（分别为5和4），这代表了与φX174 DNA相比至少有24%碱基序列错配的病毒DNA特定区域。根据相同的标准，两个碱基序列（G6和G13）似乎与φX174非常密切相关，在整个异源双链分子中产生了高度随机的单链DNA环模式，表明平均碱基序列错配几乎为24%，分布在整个分子中。这些研究结果的进化意义进行了讨论。
Many new single-stranded circular DNA-containing icosahedral phages have been isolated using a sucrose density gradient to fractionate the phages present in raw sewage into size classes. All the phages sedimenting at 120S were φX-like; from these, four different classes (called the G-phages) have been characterized. They are icosahedral particles with almost the same density and size as φX174, and they contain single-stranded circular DNA of almost the same size as the φX174 genome. Two of the phages, G4 and G14, are serologically unrelated to φX174 and are restricted by the R-factor restriction system mediated by RI endonuclease.The four new phages all code for the same number of proteins (8 or 9) as φX174, and every protein coded by the G phages has a recognizable φX174 counterpart of approximately the same molecular weight. DNA base homologies between these phages were studied by constructing heteroduplex DNA molecules with φX174 DNA and analyzing the base sequence mismatch with the electron microscope. The two phages (G4 and G14) that appeared by biological criteria and by differences in their proteins to be the most distantly related to φX174 gave heteroduplex DNA molecules with a highly characteristic and ordered pattern of single-stranded DNA loops (5 and 4, respectively), which represent specific regions of the viral DNA that have at least 24% base sequence mismatch compared with φX174 DNA. The two phages (G6 and G13) that by the same criteria appear to be very closely related to φX174, gave a highly random pattern of single-stranded DNA loops throughout the heteroduplex molecule, suggesting that the average base sequence mismatch of almost 24% is distributed throughout the whole molecule. The evolutionary significance of these findings is discussed.