IS421, a new insertion sequence in Escherichia coli.

The nucleotide sequence of a new insertion sequence (IS) in Escherichia coli, IS421, was determined. It is 1340 bp long and contains inverted repeats of 22 bp at its termini. It is flanked by 13 bp direct repeats apparently generated upon insertion. There are two ORFs longer than 200 bp in IS421. One can encode a polypeptide of 371 amino acids (aa) and the other, which is on the other strand, can encode a polypeptide of 102 aa. The C-terminal part of the 371 aa polypeptide shows some homology to that of transposases encoded in some other known IS elements. The copy number of IS421 in chromosomal DNA was 4 for E. coli K-12 and B, and 5 for E. coli C, as determined by the Southern hybridization of restriction fragments.