Kiino D R, Silhavy T J
J Bacteriol. 1984 Jun;158(3):878-83. doi: 10.1128/jb.158.3.878-883.1984.
The 42-1 lamB-lacZ gene fusion confers a conditionally lethal, export-dependent phenotype known as maltose sensitivity. A maltose-resistant mutant showing decreased beta-galactosidase activity of the hybrid protein, designated prlF1 (protein localization), was unlinked to the lamB-lacZ fusion. This mutation mapped at 70 min on the Escherichia coli linkage map and conferred maltose resistance, a 30-fold reduction in beta-galactosidase activity, and a 30% decrease in cellular growth rate at 30 degrees C that was independent of the presence of a gene fusion. prlF1 also decreased the beta-galactosidase activity and relieved the maltose sensitivity conferred by fusions of lacZ to the gene specifying the periplasmic maltose-binding protein, malE. The decrease in beta-galactosidase activity, however, was specific for exported hybrid proteins. When export of the hybrid protein was blocked by a signal sequence mutation, prlF1 decreased the beta-galactosidase activity only 2.5-fold. Similarly, prlF1 did not affect the beta-galactosidase activity of fusions of lacZ to a gene specifying a nonexported protein, malK.
42-1 lamB-lacZ基因融合赋予一种条件致死的、依赖输出的表型，称为麦芽糖敏感性。一个麦芽糖抗性突变体显示杂合蛋白的β-半乳糖苷酶活性降低，命名为prlF1（蛋白质定位），它与lamB-lacZ融合不连锁。该突变位于大肠杆菌连锁图谱的70分钟处，赋予麦芽糖抗性、β-半乳糖苷酶活性降低30倍以及在30℃时细胞生长速率降低30%，且这与基因融合的存在无关。prlF1还降低了β-半乳糖苷酶活性，并缓解了由lacZ与指定周质麦芽糖结合蛋白malE的基因融合所赋予的麦芽糖敏感性。然而，β-半乳糖苷酶活性的降低对输出的杂合蛋白具有特异性。当杂合蛋白的输出被信号序列突变阻断时，prlF1仅使β-半乳糖苷酶活性降低2.5倍。同样，prlF1不影响lacZ与指定非输出蛋白malK的基因融合的β-半乳糖苷酶活性。
