Deletion and rearrangement of plasmld DNA during transformation of Escherichia coli with linear plasmid molecules

SUtWARY When E-coli was transformed with linearized pBR322 DNA, many transformants contained recircularized plasmids bearing deletions and other rearrangements. Most aberrant molecules were monomeric but dimeric but pBR322 sequences in both direct and inverse repeat with deletions at two or more junctions. Transformation frequencies for linear DNA were drastically reduced in xth-l~ bacteria with type lib deletants predominating in transformants. Trns Indicates that exonuclease III is important for perfect recyclization of plasmids and the generation of type I deletants. In vivo recyclization of in vitro ligation products explains many of the aberrant DNA molecules that are encountered during gene cloning.