Precise Excision of IS <i>5</i> from the Intergenic Region between the <i>fucPIK</i> and the <i>fucAO</i> Operons and Mutational Control of <i>fucPIK</i> Operon Expression in <i>Escherichia coli</i>

Abstract

Excision of transposable genetic elements from host DNA occurs at low frequencies and is usually imprecise. A common insertion sequence element in Escherichia coli, IS5, has been shown to provide various benefits to its host by inserting into specific sites. Precise excision of this element had not previously been demonstrated. Using a unique system, the fucose (fuc) regulon, in which IS5 insertion and excision result in two distinct selectable phenotypes, we have demonstrated that IS5 can precisely excise from its insertion site, restoring the wild-type phenotype. In addition to precise excision, several "suppressor" insertion, deletion, and point mutations restore the wild-type Fuc(+) phenotype to various degrees without IS5 excision. The possible bases for these observations are discussed.