A novel cloning vector for the direct selection of recombinant DNA in E. coli.

A new plasmid cloning vector (pHE3) is described carrying dominant p-fluorophenylalanine-sensitivity (pheS) and chloramphenicol-resistance markers. This vector is used in combination with a p-fluorophenylalanine-resistant Escherichia coli recipient (strain RR28). Foreign DNA can be cloned into pHE3 leading to insertional inactivation of pheS. Transformation of RR28, and plating on minimal medium with chloramphenicol plus p-fluorophenylalanine (pfp) directly selects for colonies containing recombinant DNA.