Watanabe M, Blobel G
Laboratory of Cell Biology, Howard Hughes Medical Institute, Rockefeller University, New York, New York 10021.
Cell. 1989 Aug 25;58(4):695-705. doi: 10.1016/0092-8674(89)90104-9.
A purified 64 kd protein, consisting of four identical subunits of the 16 kd SecB, binds to the signal sequence of preproteins prior to their translocation across inverted vesicles (INV) derived from the E. coli plasma membrane. The purified SecB tetramer competes with canine signal recognition particle (SRP) in signal sequence binding and thus behaves as a prokaryotic equivalent of SRP. As shown by cell fractionation and immunoblot analysis with anti-SecB antibodies, SecB is a cytosolic protein. An E. coli supernatant depleted of SecB after passage through an anti-SecB Sepharose column retains full translation activity but is unable to support translocation into added INV. Translocation into INV is fully restored by readdition of purified SecB.
一种纯化的64kd蛋白质，由四个相同的16kd SecB亚基组成，在前体蛋白穿过源自大肠杆菌质膜的内翻囊泡（INV）之前，与前体蛋白的信号序列结合。纯化的SecB四聚体在信号序列结合方面与犬信号识别颗粒（SRP）竞争，因此表现为原核生物中与SRP等效的蛋白。如通过细胞分级分离和用抗SecB抗体进行免疫印迹分析所示，SecB是一种胞质蛋白。通过抗SecB琼脂糖柱后耗尽SecB的大肠杆菌上清液保留了完全的翻译活性，但不能支持向添加的INV中的转运。通过重新添加纯化的SecB，向INV中的转运完全恢复。
