Zabeau M, Friedman S, Van Montagu M, Schell J
Mol Gen Genet. 1980;179(1):63-73. doi: 10.1007/BF00268447.
Host controlled restriction in Escherichia coli can be relieved by pre-infecting restricting cells with modified lambda helper phages. This process, in which intact unmodified phage genomes are allowed to escape restriction attack, is mediated by a newly identified lambda function called ral. The ral gene has been located by deletion mapping between cIII and N. Efficient expression of the ral gene requires the product of the regulator gene N. Polyacrylamide gel analysis of the lambda proteins specified by the cIII-N region failed to reveal the product of the ral gene, but demonstrated that protein Ea10 is encoded by a gene located immediately to the left of ral. From these results the map order cIII-Ea10-ral-TL1-N was deduced. Ral specifically alleviates restriction in E. coli K and E. coli B, but does not affect restriction systems EcoRI, EcoRII and EcoP1. In addition, ral enhances the modification activity of the EcoK and EcoB restriction enzymes: we observed that efficient modification of progeny phages obtained by propagating unmodified lambda phages in r-m+ hosts, is dependent upon the presence of ral. We thus conclude that the ral gene product acts by modulating the restriction and modification activities of the type I restriction systems in E. coli, and the possible mechanisms will be discussed.
通过用修饰的λ辅助噬菌体预先感染限制细胞，可以解除大肠杆菌中的宿主控制限制。在这个过程中，完整的未修饰噬菌体基因组能够逃脱限制攻击，这是由一种新发现的λ功能ral介导的。ral基因通过缺失作图定位在cIII和N之间。ral基因的有效表达需要调节基因N的产物。对cIII - N区域指定的λ蛋白进行聚丙烯酰胺凝胶分析未能揭示ral基因的产物，但表明蛋白Ea10由紧邻ral左侧的一个基因编码。根据这些结果推断出图谱顺序为cIII - Ea10 - ral - TL1 - N。Ral能特异性地减轻大肠杆菌K和大肠杆菌B中的限制，但不影响EcoRI、EcoRII和EcoP1限制系统。此外，ral增强了EcoK和EcoB限制酶的修饰活性：我们观察到，通过在r - m +宿主中繁殖未修饰的λ噬菌体获得的子代噬菌体的有效修饰，依赖于ral的存在。因此，我们得出结论，ral基因产物通过调节大肠杆菌中I型限制系统的限制和修饰活性起作用，并将讨论可能的机制。
