On the segregation of IS1-mediated cointegrates between bacteriophage P1 DNA and plasmid pBR322 derivatives

Abstract

Considerable attention has been paid in recent years to the cointegration of two replicons mediated by mobile genetic elements in prokaryotes [1-3]. It is widely accepted that some transposons, namely Tn3 and its relatives including the IS element yd, form cointegrates as intermediates in their transposition [4-10]. These cointegrates are resolved by a site-specific recombinase encoded by the elements. Since this recombinase also acts as a repressor for its own biosynthesis [7,11], it is assumed to be present in low amounts in all cells harboring Tn3. Therefore, cointegrates are usually unstable, but stable cointegrates are obtained with mutants affected in the resolution process [4,6,7]. However, it is not yet clear whether cointegrates are also prerequisite intermediates in the transposition of other IS elements such as IS/, because cointegrates carrying IS/ as direct repeats at junctions of two replicons have been isolated without introducing a mutation in the elements [12-18]. This report describes stability and segregation processes of IS/ mediated cointegrates which had been formed between the bacteriophage P1 genome and plasmid pBR322 derivatives. 2.1. Strains and media