Mock M, Miyada C G, Collier R J
J Bacteriol. 1984 Aug;159(2):658-62. doi: 10.1128/jb.159.2.658-662.1984.
Partial deletions in the immunity gene of the colicin E3 operon were used to study possible functions of the immunity protein besides protection against exogenous colicin. Nuclease BAL-31 was used to create a series of carboxyl-terminal deletions of the immunity gene. Mutants displaying lowered immunity against exogenous colicin were found, and six that had reduced but detectable levels of immunity were chosen for further analysis. DNA sequence analysis of the deletions showed that all six terminated within the last five codons of the immunity gene. The wild-type immunity gene was replaced by each of the six mutated immunity genes in a plasmid containing an otherwise functional colicin E3 operon. Transformants containing the resulting plasmids produced smaller colonies on solid medium and grew more slowly in liquid culture than transformants carrying the wild-type colicin and immunity genes. This result suggested that immunity protein was required to protect the cell against endogenous colicin E3. This idea was confirmed in experiments in which the colicin E3 and immunity genes were independently cloned on two compatible plasmid vectors.
利用大肠杆菌素E3操纵子免疫基因的部分缺失来研究免疫蛋白除了抵御外源大肠杆菌素之外的可能功能。使用核酸酶BAL-31构建了一系列免疫基因的羧基末端缺失突变体。发现了对外源大肠杆菌素免疫性降低的突变体，并选择了六个免疫性降低但仍可检测到的突变体进行进一步分析。缺失片段的DNA序列分析表明，所有六个突变体均在免疫基因的最后五个密码子内终止。在含有功能正常的大肠杆菌素E3操纵子的质粒中，野生型免疫基因被六个突变免疫基因中的每一个所取代。与携带野生型大肠杆菌素和免疫基因的转化体相比，含有所得质粒的转化体在固体培养基上形成的菌落较小，在液体培养中生长较慢。这一结果表明，需要免疫蛋白来保护细胞免受内源性大肠杆菌素E3的侵害。在将大肠杆菌素E3和免疫基因分别克隆到两个相容质粒载体上的实验中，这一观点得到了证实。
