Enzymatic properties of the Caenorhabditis elegans Dna2 endonuclease/helicase and a species-specific interaction between RPA and Dna2

In both budding and fission yeasts, a null mutation of the DNA2 gene is lethal. In contrast, a null mutation of Caenorhabditis elegans dna2(+) causes a delayed lethality, allowing survival of some mutant C. elegans adults to F2 generation. In order to understand reasons for this difference in requirement of Dna2 between these organisms, we examined the enzymatic properties of the recombinant C. elegans Dna2 (CeDna2) and its interaction with replication-protein A (RPA) from various sources. Like budding yeast Dna2, CeDna2 possesses DNA-dependent ATPase, helicase and endonuclease activities. The specific activities of both ATPase and endonuclease activities of the CeDna2 were considerably higher than the yeast Dna2 (similar to 10- and 20-fold, respectively). CeDna2 endonuclease efficiently degraded a short 50 single-stranded DNA tail (< 10 nt) that was hardly cleaved by ScDna2. Both endonuclease and helicase activities of CeDna2 were stimulated by CeRPA, but not by human or yeast RPA, demonstrating a species-specific interaction between Dna2 and RPA. These and other enzymatic properties of CeDna2 described in this paper may shed light on the observation that C. elegans is less stringently dependent on Dna2 for its viability than Saccharomyces cerevisiae. We propose that flaps generated by DNA polymerase delta-mediated displacement DNA synthesis are mostly short in C. elegans eukaryotes, and hence less dependent on Dna2 for viability.