Characterization of Streptococcus pneumoniae PriA helicase and its ATPase and unwinding activities in DNA replication restart

DNA replication forks often encounter template DNA lesions that can stall their progression. The PriA-dependent pathway is the major replication restart mechanism in Gram-positive bacteria, and it requires several primosome proteins. Among them, PriA protein — a 3′ to 5′ superfamily-2 DNA helicase — is the key factor in recognizing DNA lesions and it also recruits other proteins. Here, we investigated the ATPase and helicase activities of Streptococcus pneumoniae PriA (SpPriA) through biochemical and kinetic analyses. By comparing various DNA substrates, we observed that SpPriA is unable to unwind duplex DNA with high GC content. We constructed a deletion mutant protein (SpPriA_deloop) from which the loop area of the DNA-binding domain of PriA had been removed. Functional assays on SpPriA_deloop revealed that the loop area is important in endowing DNA-binding properties on the helicase. We also show that the presence of DnaD loader protein is important for enhancing SpPriA ATPase and DNA unwinding activities.