About the cover

August 2015 Volume 11 No 8

A single-molecule approach using magnetic tweezers shows that DNA strand separation alone can trigger a lock at Tus–Ter sites where oppositely moving replisomes on circular bacterial chromosomes must avoid crashing. The results support a 'mousetrap' model in which replication-related proteins are not necessary and strand separation is followed by an interaction between Tus and C6 of the Ter site that sets up a hierarchy of interactions to allow the Tus–Ter complex to progressively strengthen. Cover art by Erin Dewalt, based on an image provided by TU Delft/Tremani. Article, p579; News & Views, p550