Since IS elements, by definition, do not carry other genes, they tend not to be used as genetic tools. On the other hand, mutations caused by IS's tend to be fairly common among spontaneously derived mutants, so that knowledge of their properties is relevant. In either case, MGEs are essentially pathogenic elements whose environment is the genome of the host. The former is a function of the frequency of transposition, while the latter reflects their target sites. Not surprisingly, then, MGEs spend most of their regulatory efforts trying to transpose as infrequently as possible to avoid putting their host at a selective disadvantage.
Some elements also try to aid the host by supplying useful functions like drug-resistance.
These sequences also tend to have RNA termination signals as well as nonsense codons in all three reading frames and are therefore polar. Typically they encode one large open reading frame of 300 to 400 amino acids and by definition the protein encoded by this reading frame is involved in the transposition event. Although there are exceptions, insertion sequences tend to be present in a small number of copies in the genome. For example, IS1 is present in 6 to l0 copies in E. coli chromosome while IS2 and 3 are typically present in about five copies. This restoration is probably one of the few things that do not happen in transposition.