Identification of a novel genetic element in Escherichia coli K-12

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Abstract
Induction of the SOS repair processes of E. coli K-12 caused a 14.4-kilobase species of circular DNA, called element e14, to be excised from the chromosome. To aid further characterization of this species, an 11.6-kilobase segment of e14 was inserted into the HindIII site of plasmid pBR313. To map e14 on the E. coli K-12 chromosome, the recombinant plasmid, pAG2 was used to transform a polA recipient, an event which required integration of pAG2 into the recipient chromosome. This recombinational event was dependent upon the region of homology between the incoming plasmid and the chromosome, as no transformants were scored when either a strain cured of the element was the recipient or pBR313 was the transforming DNA. These transformants showed that e14 maps between the purB and pyrC loci near min 25. Several strains of E. coli K-12 were found to contain e14; however, 1 strain, Ymel trpA36, did not. In addition, e14 was absent in both E. coli B/5 and E. coli C. The approach to mapping developed for this work could be used to map other fragments of E. coli deoxyribonucleic acid which have no known phenotype.