It is likely that the composite transposon evolved when two IS elements inserted on both sides of a gene. The IS elements flank the drug resistance gene (or other selectable marker). One or both IS elements may be functional these encode the transposition function for this class of transposons. One type of transposon, called a composite transposon, has an IS element at each end (Figure 9.10.C.). They usually encode a drug resistance gene or other marker besides the functions required for transposition (Figure 9.10.B.). Transposons are larger transposable elements, ranging in size from 2500 to 21,000 bp. The amount of transposase is well regulated and is the primary determinant of the rate of transposition. IS1, IS10, etc.Īn insertion sequence encodes a transposase enzyme that catalyzes the transposition. Each family of insertion sequence in a species is named IS followed by a number, e.g. The sequences of the inverted repeats at each end of the IS are very similar but not necessarily identical. The inverted repeats are part of the IS element itself. Note that this is different from the FDRs, which are duplications of the target site. The DNA sequence of an IS has inverted repeats (about 10 to 40 bp) at its termini (Figure 9.10A.). Different insertion sequences range in size from about 800 bp to 2000 bp. They were first recognized by the mutations they cause by inserting into bacterial genes. In bacteria, these are either short insertion sequences or longer transposons.Īn insertion sequences, or IS, is a short DNA sequence that moves from one location to another. Transposable elements that move via DNA intermediatesĪmong the most thoroughly characterized transposable elements are those that move by DNA intermediates.
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