The site-specific deletion in plasmid pBR322

The formation of a deletion derivative of plasmid pBR322, designated pBR322 delta 1, was observed during cloning of various eukaryotic DNAs, when the BamHI site of the plasmid vector was used for construction of the recombinant molecules. The restriction analysis of six independently isolated pBR322 delta 1 plasmids allowed establishment of their complete identity. Similar deletion derivatives were also formed as a result of transformation of Escherichia coli cells by the linear form of vector pBR322 produced by BamHI cleavage, but not by SalI or HindIII. The endpoints of the deletion in one of the pBR322 delta 1 plasmids occurred at positions 375 and 16666 bp from the EcoRI site, as determined by sequence analysis. Formation of pBR322 delta 1 is most probably due to site-specific recombination between the sequence in the 1666-1670 bp region and the BamHI end of the linear pBR322 molecule. THe deletion was not controlled by the recA system of the host bacteria.