The CloneJET PCR cloning kit contains a ready-to-use positive selection cloning vector pJET1.2/blunt. The vector contains a lethal restriction enzyme gene that is disrupted by ligation of a DNA insert into the cloning site. As a result, only bacterial cells with recombinant plasmids are able to form colonies. Recircularised pJET1.2/blunt vector molecules lacking an insert express a lethal restriction enzyme, which kills the host E. coli cell after transformation. This positive selection drastically accelerates the process of colony screening and eliminates additional costs required for blue/white selection.