IS30, a new insertion sequence of Escherichia coli K12

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Abstract
Summary Three independent spontaneous mutations of prophage P1 affecting the ability of the phage to reproduce vegetatively are due to the insertion of a mobile genetic element, called IS 30. The same sequence is also carried in the R plasmid NR 1-Basel, but not in the parental plasmid NR 1. Southern hybridisation study indicates that the Escherichia coli K 12 chromosome carries several copies of IS 30 as a normal resident. IS 30 is 1.2 kb long and contains unique restriction cleavage sites for Bg/II, ClaI, HindIII, NciI and HincII, and it is cleaved twice by the enzymes HpaII and TaqI. The ends of IS 30 are formed by 26 bp long inverted repeats with 3 bases mismatched. Upon transposition IS 30 generates a duplication of only 2 bp of the target. The following observations suggest a pronounced specificity in target selection by IS 30. In transposition to the phage P 1 genome a single integration site was used three times independently, and in both orientations. A short region of sequence homology has been identified between the P 1 and NR 1-Basel insertion sites. IS 30 has mediated cointegration as well as deletion. The entire IS 30 sequences were duplicated in the cointegrates between a pBR 322 derivative containing IS 30 and the genome of phage P 1–15, and several loci on the P1–15 genome served as fusion sites, some of which were used more than once.