IS1H (Zhao and Hill, 1995) is part of the RhsF element present in Escherichia coli ECOR50, but not in K12. The Rhs elements comprise a family of large accessory sequences found in certain E. coli strains. Their role and function remain unknown. There is a nt apparently "missing" at position 521 of IS1H. For comparison purposes, this shift has been ignored: thus insB ORF is a fusion between two ORFs: 72 aa (306-521) and 75 aa (521-750). This feature remains to be confirmed. Note that on the virulence plasmid pO157 of Escherichia coli O157:H7 strain EDL933, 304 bp downstream of the espP gene (encoding an extracellular serine protease shown to cleave the human coagulation factor V, therefore contributing to the mucosal haemorrhage observed in patients with haemorrhagic colitis), a 491-bp inactive IS1-like element was shown to display 92 % identity with IS1H (Brunder et al., 1997, Accession number: X97542).