Josefsson L G, Hardy S, Harayama S, Randall L
Ann Microbiol (Paris). 1982 Jan;133A(1):111-4.
Two proteins encoded in the malB locus, the maltose-binding protein and the LamB protein, are exported to the periplasm and outer membrane, respectively. Both proteins are synthesized on membrane-bound polysomes in precursor forms which contain signal sequences at their amino-termini. Proteolytic removal of the signal sequence from maltose-binding protein begins co-translationally but is nat initiated until the nascent chains have attained 80% of their final length. Approximately one-third of the molecules are processed co-translationally, the remainder being processed post-translationally. In contrast, the LamB precursor is processed almost entirely post-translationally. In neither case is it clear when the polypeptide chains are transferred through the cytoplasmic membrane. An interesting feature with as yet unknown significance is the non-uniform rate of elongation of maltose-binding protein. The export of maltose-binding protein and the lamB protein as well as that of other proteins, has been shown to require an energized membrane.
由malB基因座编码的两种蛋白质，即麦芽糖结合蛋白和LamB蛋白，分别被转运到周质和外膜。这两种蛋白质都是以前体形式在膜结合多核糖体上合成的，其氨基末端含有信号序列。麦芽糖结合蛋白信号序列的蛋白水解去除在共翻译过程中开始，但直到新生链达到其最终长度的80%才开始。大约三分之一的分子在共翻译过程中被加工，其余的在翻译后被加工。相比之下，LamB前体几乎完全在翻译后被加工。在这两种情况下，多肽链何时穿过细胞质膜尚不清楚。麦芽糖结合蛋白伸长率不均匀这一有趣特征的意义尚不清楚。麦芽糖结合蛋白和LamB蛋白以及其他蛋白质的输出已被证明需要有能量的膜。
