Duplex opening by primosome protein PriA for replisome assembly on a recombination intermediate

Area of Science:

• Molecular Biology
• Virology
• DNA Replication

Background:

• Bacteriophage Mu replication relies on the Escherichia coli replisome, involving proteins like PriA and the DnaB helicase.
• MuA transposase creates replication forks, but these initially lack the single-stranded DNA required for DnaB loading.
• PriA is known to assemble primosomes and recruit DnaB, but its role at Mu replication forks was unclear.

Purpose of the Study:

• To investigate the mechanism by which PriA facilitates DnaB loading and initiates replication at bacteriophage Mu replication forks.
• To determine the role of PriA's helicase activity in creating a DnaB binding site on Mu-induced forked DNA structures.

Main Methods:

• In vitro assays using synthetic forked DNA substrates to study PriA binding and helicase activity.
• Analysis of PriA's interaction with MuA-generated forked DNA structures.
• Assessment of PriA's ability to promote preprimosome assembly and DnaB loading.
• In vivo and in vitro experiments using wild-type and mutant PriA proteins to evaluate Mu DNA replication.

Main Results:

• PriA binds to MuA-generated forked DNA structures and utilizes its helicase activity to unwind the duplex DNA.
• This unwinding action by PriA creates the necessary single-stranded DNA site for DnaB loading onto the lagging strand template.
• PriA translocates along the DNA, facilitating DnaB loading and initiating replication fork progression.
• Mutant PriA lacking helicase activity failed to promote DnaB loading and impaired Mu DNA replication.

Conclusions:

• PriA's helicase activity is critical for initiating bacteriophage Mu DNA replication by generating a DnaB binding site.
• PriA functions as a mobile initiator, coupling helicase and primosome assembly functions to overcome replication blockages.
• This mechanism ensures efficient replisome assembly and minimizes interruptions during chromosomal replication.