pMAL-c2x载体

pMAL™系统是一种高效的蛋白融合表达及纯化系统。pMAL载体含有编码麦芽糖结合蛋白（Maltose Binding Protein, MBP）的大肠杆菌malE基因，其下游的多克隆位点便于目的基因插入，表达N端带有MBP的融合蛋白。通过"tac"强启动子和malE翻译起始信号使克隆基因获得高效表达，并进一步利用MBP对麦芽糖的亲和性达到用Amylose柱对融合蛋白的一步亲和纯化。

The system uses the pMAL vectors which are designed so that insertion interrupts a lacZα gene allowing a blue-to-white screen for inserts on X-gal (5). pMAL-c2 series has an exact deletion of the malE signal sequence, resulting in cytoplasmic expression of the fusion protein. pMAL-p2 series contains the normal malE signal sequence, which directs the fusion protein through the cytoplasmic membrane. pMAL-p2 fusion proteins capable of being exported can be purified from the periplasm. Between the malE sequence and the polylinker there is a spacer sequence coding for 10 asparagine residues. This spacer insulates MBP from the protein of interest, increasing the chances that a particular fusion will bind tightly to the amylose resin. The vectors also include a sequence coding for the recognition site of a specific protease. This allows the protein of interest to be cleaved from MBP after purification, without adding any vector-derived residues to the protein (6). For this purpose, the polylinker includes a restriction site superimposed on the sequence coding for the site of the specific protease. This is where the gene of interest is inserted. An EcoR I site in the same reading frame as that of λgt11 and a number of other useful sites are present directly downstream. The vectors also include the M13 origin of DNA replication which allows the production of single-stranded DNA for sequencing and mutagenesis by infecting with M13KO7 helper phage (NEB #N0315S).