Silverman M, Zieg J, Hilmen M, Simon M
Proc Natl Acad Sci U S A. 1979 Jan;76(1):391-5. doi: 10.1073/pnas.76.1.391.
The alternative expression of Salmonella genes H1 and H2, which specify different flagellar antigens, results in the oscillation of phenotype known as phase variation. This alternation is controlled by the inversion of an 800-base-pair sequence of DNA adjacent to, or including part of, the H2 gene. The invertable region was presumed to regulate the function of a promoter and to include specific sites at which a recombinational event, resulting in the inversion, could occur. Here we report genetic manipulations of hybrid lambda phage carrying the H2 gene that were used to define the H2 promoter region and the recombinational sites. The H2 gene fragment was inserted on a hybrid lambda phage next to the cheW gene, which lacked a promoter element. In the resulting fusion, cheW gene activity was restored, the expression of the H2 and cheW genes was controlled coordinately by the inversion, and the polarity of transcription and location of the H2 gene could be determined. Evidence from this type of gene fusion suggested that the H2 gene promoter is included in the inversion region. Hybrid H2 phage were constructed that contained substitutions for regions of the H2 gene. In contrast to hybrid lambda containing the H2 gene, which alternate between "on" and "off" states, several substituted lambdaH2 were fixed in the "on" state. A site necessary for the recombinational event must have been removed in these fixed lambdaH2.
沙门氏菌H1和H2基因的交替表达可产生不同的鞭毛抗原，从而导致表型振荡，即相变。这种交替由与H2基因相邻或包含其部分序列的一段800个碱基对的DNA序列的倒位控制。推测该可倒位区域调节启动子的功能，并包含可发生导致倒位的重组事件的特定位点。在此，我们报告了携带H2基因的杂交λ噬菌体的基因操作，这些操作被用于确定H2启动子区域和重组位点。将H2基因片段插入到一个杂交λ噬菌体上，紧挨着缺乏启动子元件的cheW基因。在产生的融合体中，cheW基因活性得以恢复，H2和cheW基因的表达通过倒位进行协同控制，并且可以确定H2基因的转录极性和位置。这种基因融合的证据表明，H2基因启动子包含在倒位区域内。构建了含有H2基因区域替代物的杂交H2噬菌体。与含有H2基因的杂交λ噬菌体在“开”和“关”状态之间交替不同，几个替代的λH2固定在“开”状态。在这些固定的λH2中，重组事件所必需的位点必定已被去除。
