This dissertation describes the purification and characterization of a host factor necessary for conversion of the bacteriophage Mu STC2 transpososome to a primosome. The identification of the Escherichia coli translation initiation factor IF2-2 as a key component of Mu replicative transposition suggests that the significance of the transition mechanism involved in converting the Mu transpososome to a replisome is not limited to the coordination of DNA recombination with replication but also provides potential mechanisms by which these fundamental cellular processes interface with cell physiology.

Bacteriophage Mu is a temperate phage that propagates its DNA through transposition. Phage-encoded MuA transposase binds to the ends of the Mu genome and assembles into a stable transpososome, which catalyzes strand transfer to target DNA to form a forked structure at each end that are held together in a synaptic complex. E. coli molecular chaperone protein ClpX destabilizes the tightly bound transpososome at the Mu forks. A partially purified bacterial fraction, designated Mu Replication Factor alpha 2 (MRF alpha 2) promotes the disassembly of the transpososome and the orderly transition to a replisome assembled with the DNA polymerise III holoenzyme and the restart primosome, the same set of proteins used by the host to reactivate arrested replication forks.

A dissection of MRF alpha 2 reveals that separate components catalyze at least two distinct steps. MRF alpha-Disassembly Factor (MRF alpha-DF) removes the MuA transposase of the STC2 transpososome and assembles a new nucleoprotein complex. MRF alpha-Prereplisome (MRF alpha-PR) further modifies this complex to facilitate primosome assembly by a PriA-PriC pathway that requires PriA helicase function. MRF alpha-PR has been purified to homogeneity and has been identified by tandem MS/MS as E. coli translation initiation factor IF2. Purification and characterization of a naturally occurring isoform, 1F2-2, has shown that 1F2-2 is a necessary and sufficient component of MRF alpha-PR. Experimental results indicate that MRFα-DF and IF2-2 work together to support the stepwise remodeling of Mu transposition intermediates and their associated proteins to tightly regulate accessibility of the Mu fork to specific host factors that determine the pathway of replisome assembly by replication restart proteins.