| Summary: | <p>Abstract</p> <p>Background</p> <p>Bacterial DNA replication restart pathways facilitate reinitiation of DNA replication following disruptive encounters of a replisome with DNA damage, thereby allowing complete and faithful duplication of the genome. In <it>Neisseria gonorrhoeae</it>, the primosome proteins that catalyze DNA replication restart differ from the well-studied primosome proteins of <it>E. coli </it>with respect to the number of proteins involved and the affinities of their physical interactions: the PriA:PriB interaction is weak in <it>E. coli</it>, but strong in <it>N. gonorrhoeae</it>, and the PriB:DNA interaction is strong in <it>E. coli</it>, but weak in <it>N. gonorrhoeae</it>. In this study, we investigated the functional consequences of this affinity reversal.</p> <p>Results</p> <p>We report that <it>N. gonorrhoeae </it>PriA's DNA binding and unwinding activities are similar to those of <it>E. coli </it>PriA, and <it>N. gonorrhoeae </it>PriA's helicase activity is stimulated by its cognate PriB, as it is in <it>E. coli</it>. This finding is significant because <it>N. gonorrhoeae </it>PriB's single-stranded DNA binding activity is weak relative to that of <it>E. coli </it>PriB, and in <it>E. coli</it>, PriB's single-stranded DNA binding activity is important for PriB stimulation of PriA helicase. Furthermore, a <it>N. gonorrhoeae </it>PriB variant defective for binding single-stranded DNA can stimulate PriA's helicase activity, suggesting that DNA binding by PriB might not be important for PriB stimulation of PriA helicase in <it>N. gonorrhoeae</it>. We also demonstrate that <it>N. gonorrhoeae </it>PriB stimulates ATP hydrolysis catalyzed by its cognate PriA. This activity of PriB has not been observed in <it>E. coli</it>, and could be important for PriB stimulation of PriA helicase in <it>N. gonorrhoeae</it>.</p> <p>Conclusions</p> <p>The results of this study demonstrate that a bacterial PriB homolog with weak single-stranded DNA binding activity can stimulate the DNA unwinding activity of its cognate PriA helicase. While it remains unclear if <it>N. gonorrhoeae </it>PriB's weak DNA binding activity is required for PriB stimulation of PriA helicase, the ability of PriB to stimulate PriA-catalyzed ATP hydrolysis could play an important role. Thus, the weak interaction between <it>N. gonorrhoeae </it>PriB and DNA might be compensated for by the strong interaction between PriB and PriA, which could result in allosteric activation of PriA's ATPase activity.</p>
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