In vivo intermolecular recombination in Escherichia coli: application to plasmid constructions.

Repair of a double-strand break (DSB) was investigated by intermolecular recombination in Escherichia coli (Ec) recBC sbcBC cells with restriction enzyme-cleaved model plasmids. Circular plasmids were generated when a linearized plasmid (vector) containing an origin of replication was co-transformed with a DNA fragment (template) containing a homologous sequence. The influence of the position of the DSB in the vector was analyzed using templates which contain various genetic markers, non-homologous sequences and/or deletions relative to the vector. In all cases, when a DSB occurs within a marker, this marker is lost in the resulting plasmid, whereas markers flanked by homologous regions located in the vicinity of a DSB are transmitted. Insertions (deletions), substitutions and shuffling of genetic markers are possible by in vivo recombination using Ec and can be applied to plasmid constructions. It is shown that recombination can occur from both template ends or from one vector and one template end. A D-loop nuclease is suggested to participate in the resolution of the recombination intermediates.