Brandt U, Yu L, Yu C A, Trumpower B L
Department of Biochemistry, Dartmouth Medical School, Hanover, New Hampshire 03755.
J Biol Chem. 1993 Apr 25;268(12):8387-90.
The amino acid sequence of subunit 9 of the bovine heart cytochrome bc1 complex is identical to the 78-amino acid presequence that is removed post-translationally from the Rieske iron-sulfur protein as it is imported and targeted to the mitochondrial cytochrome bc1 complex. Iron-sulfur protein precursor, generated by in vitro transcription and translation, is processed to mature size in a single step when incubated with rat liver mitochondria, and generates a peptide that comigrates on SDS-polyacrylamide gel electrophoresis with subunit 9. These results suggest that the Rieske protein is processed in a single proteolytic step after it is inserted into the cytochrome bc1 complex in mammals, and that the processed presequence remains as a subunit of the complex. This is apparently the first instance in which a cleaved targeting presequence has been shown to be retained in the cell, possibly exhibiting a second function in addition to its function in protein trafficking.
牛心细胞色素bc1复合物亚基9的氨基酸序列与78个氨基酸的前导序列相同，该前导序列在翻译后从 Rieske 铁硫蛋白中去除，因为它被导入并靶向线粒体细胞色素bc1复合物。通过体外转录和翻译产生的铁硫蛋白前体，与大鼠肝线粒体一起孵育时，在一步中被加工成成熟大小，并产生一种在SDS-聚丙烯酰胺凝胶电泳上与亚基9共迁移的肽。这些结果表明，Rieske 蛋白在插入哺乳动物细胞色素bc1复合物后，在单一的蛋白水解步骤中被加工，并且加工后的前导序列作为复合物的一个亚基保留下来。这显然是首次证明切割后的靶向前导序列在细胞中被保留，可能除了在蛋白质运输中的功能外，还发挥第二种功能。
