Copy-out–Paste-in Transposition of IS 911 : A Major Transposition Pathway

Abstract

ABSTRACT IS 911 has provided a powerful model for studying the transposition of members of a large class of transposable element: the IS 3 family of bacterial Insertion Sequences (IS). These transpose by a Copy-out–Paste-in mechanism in which a double-strand IS circle transposition intermediate is generated from the donor site by replication and proceeds to integrate into a suitable double strand DNA target. This is perhaps one of the most common transposition mechanisms known to date. Copy-out–Paste-in transposition has been adopted by members of at least eight large IS families. This chapter details the different steps of the Copy-out–Paste-in mechanism involved in IS 911 transposition. At a more biological level it also describes various aspects of regulation of the transposition process. These include transposase production by programmed translational frameshifting, transposase expression from the circular intermediate using a specialized promoter assembled at the circle junction and binding of the nascent transposase while it remains attached to the ribosome during translation (co-translational binding). This co-translational binding of the transposase to neighboring IS ends provides an explanation for the longstanding observation that transposases show a cis -preference for their activities.