Studies of conducted trg plasmid containing unidentified DNA insert

Abstract

An unidentified DNA segment which seems to be an insertion sequence element was isolated from E. coli K12 strain. It was inserted into the hybrid plasmid consisting of pBR322 and trg gene which codes for E. coli chemosensory transduer during the transfer of chromosomal trg mutation to plasmid via Hfr-mediated conduction. The size of the undentified DNA segment was estimated to be about 1.5 Kilobase pairs, and its restriction map was constructed. It has one Bgl II and one Hind III restriction enzyme cleavage sites. The integration frequency of the plasmid containg undentified segment into the chromosome of Hfr polAts strain of E. coli was 10,000 times greater than the plamsid without any inserted segment. The frequency was even greater than that of the plasmid containing 3.4 kb DNA originated from E. coli chromosome. This implies that the unidentified DNA segment increases the frequency of recombination between the plasmid and thechromosome probably due to the presence of DNA sequence homologous to the chromosome. It is likely that the segment is a previously unidentified insertion sequence translocated from the chromosome of E. coli by illegitimate recombination. The identity of the segment remains to be discovered.