Emr S D, Schwartz M, Silhavy T J
Proc Natl Acad Sci U S A. 1978 Dec;75(12):5802-6. doi: 10.1073/pnas.75.12.5802.
Two mutant strains of Escherichia coli have been isolated in which the cellular location of an outer membrane protein, the phage lambda receptor (the lamB gene product), is altered. These mutations were initially selected in a strain containing a lamB-lacZ fusion. In the parent strain the protein coded for by the hybrid gene is located, at least in part, in the outer membrane. In the mutants it is located in the cytoplasm. The mutations responsible for the alteration of cellular location lie very early in the lamB gene, in a region corresponding to the NH2-terminus of the lambda receptor protein. One of these mutations is a small deletion internal to the lamB gene. When this mutation is present in an otherwise wild-type lamB gene, the protein produced is of lower molecular weight than normal receptor. The other mutation behaves as a point mutation; when it is present in an otherwise normal lamB gene, reversion can be demonstrated. The molecular weight of this mutant protein, which is located in the cytoplasm, is larger than that of the wild-type gene product by approximately 2000. It is suggested that these two mutations are in the portion of the lamB gene coding for a signal sequence and thereby block export of the protein.
已分离出两株大肠杆菌突变株，其中一种外膜蛋白（噬菌体λ受体，即lamB基因产物）的细胞定位发生了改变。这些突变最初是在含有lamB - lacZ融合基因的菌株中筛选出来的。在亲本菌株中，杂合基因编码的蛋白质至少部分位于外膜。而在突变株中，它位于细胞质中。导致细胞定位改变的突变位于lamB基因的非常早期，在与λ受体蛋白的NH2末端相对应的区域。其中一个突变是lamB基因内部的一个小缺失。当这个突变存在于其他方面为野生型的lamB基因中时，产生的蛋白质分子量比正常受体低。另一个突变表现为点突变；当它存在于其他方面正常的lamB基因中时，可以观察到回复突变。这种位于细胞质中的突变蛋白的分子量比野生型基因产物大约大2000。有人认为这两个突变位于lamB基因编码信号序列的部分，从而阻断了蛋白质的输出。
