The ISCR elements database

(from the website)

ISCR (Insertion Sequence Common Region) elements are Insertion sequences that have similarities to the IS91 family in both structure and function. These two insertion sequence families have several important features that are unique among IS elements: their terminal sequences are unrelated to each other instead of being inverted repeats; their transposases lack the normal DDE amino acid motif found in the majority of IS elements transposases; they do not generate directly repeated sequence on insertion. The IS91 family consists of three members IS91, IS801 and IS1294 and the ISCR family currently has 19 members ISCR1-19. Analysis of the genetic loci of the various ISCR elements has revealed that the vast majority of these elements are found in close association with antimicrobial resistance genes that are not the normal complement of the host genome. They are thus implicated in the acquisition of these genes and appear to have a specialisation for resistance gene transposition.

http://medicine.cf.ac.uk/en/research/research-groups/i3/research/antibacterial-agents/iscr-elements/