The Tn21 subgroup of bacterial transposable elements.

Abstract The Tn 3 family of transposable elements is probably the most successful group of mobile DNA elements in bacteria: there are many different but related members and they are widely distributed in gram-negative and gram-positive bacteria. The Tn 21 subgroup of the Tn 3 family contains closely related elements that provide most of the currently known variation in Tn 3 -like elements in gram-negative bacteria and that are largely responsible for the problem of multiple resistance to antibiotics in these organisms. This paper reviews the structure, the mechanism of transposition, the mode of acquisition of accessory genes, and the evolution of these elements.