[Insertion sequence common region element: a novel gene-capturing system in bacteria--a review].

Insertion sequence common region (ISCR) elements are insertion sequences that have similarities to the IS91 family in both structure and function. ISCR elements differ from the insertion sequences by that they lack terminal inverted repeats (IRs), do not generate directly repeated sequence on insertion and are thought to be transposed by a mechanism termed rolling-circle (RC) transposition. ISCR elements, as a novel gene-capturing system, can mobilize any piece of adjacent DNA sequences. This powerful gene mobilization mechanism provides antibiotic resistance genes with a highly mobile genetic vehicle to transfer between different species of bacteria. Nineteen members of the ISCR family have been discovered until now in many Gram-negative pathogens. The majority of these elements are found to be closely associated with antimicrobial resistance genes that are not necessary components of the host genome, suggesting that ISCR elements may be responsible for the rapid transmission of bacterial multi-drug resistance. This review described some important aspects of ISCR elements, including their structure characteristics, classification, mobilization mechanism, origins and evolutions.