IS organization

In addition to being small, insertion sequences are genetically compact (Fig 1.25.1). They generally encode no functions other than those involved in their mobility although individual members of several families which include additional genes are now being identified. IS-encoded functions include factors required in cis, in particular recombinationally active DNA sequences which define the ends of the element together with an enzyme, the transposase (Tpase), which recognises and processes these ends. The Tpase is generally encoded by a single or perhaps two, open reading frames and consumes nearly the entire length of the element.