New ccdB positive-selection cloning vectors with kanamycin or chloramphenicol selectable markers.

Recently, we described pKIL18/19 positive-selection cloning vectors which rely on the inactivation of the cytotoxic ccdB gene [Bernard et al., Gene 148 (1994) 71-74]. They are new tools for simplifying gene cloning/sequencing procedures, as only recombinant DNA allow the formation of viable colonies. To enhance positive-selection capabilities, putative translational reinitiation codons located within the pKIL18/19 ccdB were modified by site-directed mutagenesis. New pKIL-derived vectors with kanamycin (KmR) or chloramphenicol (CmR) resistance-encoding genes were also constructed. In addition, a new host derived from the DH2 strain was developed.