Replication of Bacteriophage Mu: Direction and Possible Location of the Origin

Abstract

The temperate bacteriophage Mu-1 is distinct from other temperate phages like λ and P2 in the way it integrates in the DNA of its host E.coli. It does so by linear insertion of its DNA without any site-specificity into the bacterial chromosome, thus causing mutations (1,2,3). Also replication of Mu is very different: in contrast to λ and P2 circular DNA molecules of genome size have never been found during lytic development of the phage. However, the existence of larger covalently closed DNA molecules, containing both Mu- and host DNA sequences, has been demonstrated (4,5). As these structures are first found at 15–20 minutes after induction as well as infection (4,5), while the Mu specific DNA synthesis already starts at 8–10 minutes (6), it seems reasonable to assume these circles are not formed until at least one round of replication has been finished.