Puohiniemi R, Simonen M, Muttilainen S, Himanen J P, Sarvas M
Department of Molecular Bacteriology, National Public Health Institute, Helsinki, Finland.
Mol Microbiol. 1992 Apr;6(8):981-90. doi: 10.1111/j.1365-2958.1992.tb02164.x.
When the genes coding for the outer membrane (OM) proteins OmpA and OmpF of Escherichia coli are fused to a signal sequence of a bacillar exoenzyme and expressed in Bacillus subtilis they remain cell-bound and the signal sequence is not cleaved. To identify the step of arrest in the export of these proteins we studied their accessibility to protease applied to intact protoplasts; they remained resistant indicating fully intracellular localization. Both proteins appeared associated with the cell membranes in sedimentation and flotation centrifugation experiments. However, OmpA and OmpF proteins synthesized in B. subtilis without a signal sequence were similarly associated with membranes in centrifugation experiments whereas electron microscopy showed the presence of intracytoplasmic inclusion bodies not obviously attached to the cytoplasmic membrane. We conclude that OmpA and OmpF proteins even when provided with a functional signal sequence do not enter the export pathway in B. subtilis, probably owing to lack of a specific export component in B. subtilis.
当编码大肠杆菌外膜（OM）蛋白OmpA和OmpF的基因与一种芽孢杆菌外切酶的信号序列融合，并在枯草芽孢杆菌中表达时，它们仍与细胞结合，且信号序列未被切割。为了确定这些蛋白质输出过程中的阻滞步骤，我们研究了它们对应用于完整原生质体的蛋白酶的可及性；它们仍具有抗性，表明完全定位于细胞内。在沉降和浮选离心实验中，这两种蛋白质似乎都与细胞膜相关。然而，在没有信号序列的情况下在枯草芽孢杆菌中合成的OmpA和OmpF蛋白在离心实验中同样与膜相关，而电子显微镜显示存在胞质内包涵体，这些包涵体并未明显附着于细胞质膜。我们得出结论，即使OmpA和OmpF蛋白具有功能性信号序列，它们在枯草芽孢杆菌中也不会进入输出途径，这可能是由于枯草芽孢杆菌中缺乏特定的输出成分。
