Positive selection of recombinant plasmids based on the EcoK restriction activity of Escherichia coli K-12

We have constructed a pTZ19R-derived vector which allows efficient positive selection of recombinant plasmids. The system uses the EcoK restriction activity of Escherichia coli K-12 to select against non-recombinant plasmids. The vector contains an EcoK site which, if deleted or disrupted by ligating a DNA fragment, yields recombinant plasmids that are no longer susceptible to EcoK restriction when transformed into a restriction-proficient E. coli host.