Opposing Roles for Two Molecular Forms of Replication Protein A in Rad51-Rad54-Mediated DNA Recombination in Plasmodium falciparum

The bacterial RecA protein and its eukaryotic homologue Rad51 play a central role in the homologous DNA strand exchange reaction during recombination and DNA repair. Previously, our lab has shown that PfRad51, the Plasmodium falciparum homologue of Rad51, exhibited ATPase activity and promoted DNA strand exchange in vitro. In this study, we evaluated the catalytic functions of PfRad51 in the presence of putative interacting partners, especially P. falciparum homologues of Rad54 and replication protein A. PfRad54 accelerated PfRad51-mediated pairing between single-stranded DNA (ssDNA) and its homologous linear double-stranded DNA (dsDNA) in the presence of 0.5 mM CaCl(2). We also present evidence that recombinant PfRPA1L protein serves the function of the bacterial homologue single-stranded binding protein (SSB) in initiating homologous pairing and strand exchange activity. More importantly, the function of PfRPA1L was negatively regulated in a dose-dependent manner by PfRPA1S, another RPA homologue in P. falciparum. Finally, we present in vivo evidence through comet assays for methyl methane sulfonate-induced DNA damage in malaria parasites and accompanying upregulation of PfRad51, PfRad54, PfRPA1L, and PfRPA1S at the level of transcript and protein needed to repair DNA damage. This study provides new insights into the role of putative Rad51-interacting proteins involved in homologous recombination and emphasizes the physiological role of DNA damage repair during the growth of parasites.