Abstract
In the lysogenic state, bacteriophage P1 is maintained as a low copy-number circular plasmid. Site-specific recombination at loxP by the phage-encoded Cre protein keeps P1 monomeric, thus helping to ensure stable plasmid inheritance. Two Escherichia coli DNA-binding proteins, PepA and ArgR, were recently reported to be necessary for maintenance or establishment of P1 lysogeny. PepA and ArgR bind to regulatory DNA sequences upstream of the ColE1 cer recombination site to regulate site-specific recombination by the XerCD recombinases. This recombination keeps ColE1 in a monomeric state and helps to ensure stable plasmid maintenance. It has been suggested that ArgR and PepA play a similar role in P1 maintenance, regulating Cre recombination by binding to DNA sequences upstream of loxP. Here, we show that ArgR does not bind to its proposed binding site upstream of loxP, and that Cre recombination at loxP in its natural P1 context is not affected by PepA and ArgR in vitro. When sequences upstream of loxP were mutated to allow ArgR binding, PepA and ArgR still had no effect on Cre recombination. Our results demonstrate that PepA requires specific DNA sequences for binding, and that PepA and ArgR have no direct role in Cre recombination at P1 loxP.
Highlights
In the lysogenic state, bacteriophage P1 is maintained as a low copy-number circular plasmid
Recombination is regulated by the accessory proteins PepA and ArgR, which bind to approximately 180 bp of accessory sequences adjacent to the cer core
The Xer recombinases are inactive at the cer core in the absence of accessory proteins, and are activated by PepA and ArgR binding to the accessory sequences
Summary
Bacteriophage P1 is maintained as a low copy-number circular plasmid. By placing loxP adjacent to appropriate DNA sequences, Cre recombination can be made to form specific topologically complex products (Gourlay and Colloms, 2004; Kilbride et al, 1999).
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