McFarland L, Francetić O, Kumamoto C A
Department of Molecular Biology and Microbiology, Tufts University School of Medicine, Boston, Massachusetts 02111.
J Bacteriol. 1993 Apr;175(8):2255-62. doi: 10.1128/jb.175.8.2255-2262.1993.
The Escherichia coli SecB protein is a cytosolic chaperone protein that is required for rapid export of a subset of exported proteins. To aid in elucidation of the activities of SecB that contribute to rapid export kinetics, mutations that partially suppressed the export defect caused by the absence of SecB were selected. One of these mutations improves protein export in the absence of SecB and is the result of a duplication of SecA coding sequences, leading to the synthesis of a large, in-frame fusion protein. Unexpectedly, this mutation conferred a second phenotype. The secA mutation exacerbated the defective protein export caused by point mutations in the signal sequence of pre-maltose-binding protein. One explanation for these results is that the mutant SecA protein has sustained a duplication of its binding site(s) for exported protein precursors so that the mutant SecA is altered in its interaction with precursor molecules.
大肠杆菌SecB蛋白是一种胞质伴侣蛋白，是一部分输出蛋白快速输出所必需的。为了有助于阐明SecB有助于快速输出动力学的活性，选择了部分抑制因SecB缺失导致的输出缺陷的突变。其中一个突变在SecB缺失的情况下改善了蛋白质输出，是SecA编码序列重复的结果，导致合成了一种大的、读框内融合蛋白。出乎意料的是，这个突变赋予了第二种表型。secA突变加剧了由前麦芽糖结合蛋白信号序列中的点突变引起的缺陷蛋白输出。对这些结果的一种解释是，突变的SecA蛋白其输出蛋白前体的结合位点发生了重复，因此突变的SecA与前体分子的相互作用发生了改变。
