PARTICIPATION OF THE BACTERIOPHAGE-MU-A PROTEIN AND HOST FACTORS IN THE INITIATION OF MU-DNA-SYNTHESIS IN-VITRO

During bacteriophage Mu transposition, strand transfer is catalyzed in the presence of phage-encoded A and B proteins and Escherichia coli H U protein, attaching Mu ends to target DNA and creating an intermediat e in transposition. Bacteriophage Mu A protein, which remains tightly bound to the Mu ends in the native strand-transfer intermediate, block ed initiation of Mu DNA replication by a system of 8 host proteins (Dn aB helicase, DnaC protein, DnaG primase, DNA polymerase III holoenzyme , DNA polymerase I, DNA gyrase, DNA ligase, and single-strand binding protein). This 8-protein system had all enzymatic activities to conver t the deproteinized intermediate to a cointegrate; however, additional host factor(s) were required to replicate the native intermediate. Wh ile replication of the native intermediate absolutely required DnaB he licase, DnaC protein, and DNA polymerase III holoenzyme, the specific requirements were relaxed for the deproteinized intermediate. Other ho st factors were able to replace these specific factors. These results indicate that Mu A protein, in conjunction with additional host factor (s), acts to promote assembly of specific host replication proteins at the Mn replication fork. This process may alter the stable interactio n of Mu A protein with the ends to allow initiation of Mu DNA synthesi s.