Sequence Analysis at IS1 Insertion Sites: Models for Transposition

Transposable elements are distinct DNA segments that can move from one site to another in bacterial or phage genomes. This transposition is site-specific with respect to the terminal sequences of the element and does not require the bacterial recA function. Integrations of the simplest of these elements, the 770-bp element, IS1, have been analyzed by nucleotide sequencing techniques (Calos et al. 1978; Grindley 1978). These studies demonstrated that insertion of IS1 at a number of sites in Escherichia coli DNA resulted in duplication of a 9-bp sequence that was present once in the wild-type sequence; a copy of this 9-bp sequence appears in the same orientation at each end of the inserted element.