Early attempts to design vehicles for the cloning of foreign DNA produced vectors that were too big, unstable, or unselectable. The tide turned in 1977 with the construction of pBR313, the direct ancestor of the well-known pBR322, which forms the basis of many vectors that are still used extensively today.1 However, the cloning systems introduced in the last year or so seem to be about as related to pBR313 as Ferraris are to little red Radio Flyer wagons. Some of the new protein expression systems allow an easily trackable component to be attached to the protein of interest to facilitate purification or other analyses. Others involve a melange of expression and purification features in a package that allows rapid shuttling of a gene of interest from scenario to scenario.
The first generation of Escherichia coli expression vectors produced an in-frame fusion of the gene of interest and lacZ.2 ß-galactosidase assays ...
