Crystal structure of the Pyrococcus horikoshii DNA primase-UTP complex:: implications for the mechanism of primer synthesis

Background: In chromosomal DNA replication, DNA primase initiates the synthesis of a dinucleotide on a single-stranded template DNA, and elongates it to form a primer RNA for the replicative DNA polymerase. Although the apo-structure of an archaeal primase has been reported, the mechanism of primer synthesis by the eukaryotic-type primase still remains to be elucidated. Results: In this study, we present the crystal structure of the eukaryotic-type DNA primase from the hyperthermophilic archaeon (Pyrococcus horikoshii) with the uridine 5'-triphosphate (UTP). In the present primase-UTP complex, the primase binds the triphosphate moiety of the UTP at the active site, which includes Asp95, Asp97, and Asp280, the essential residues for the nucleotidyl transfer reaction. Conclusion: The nucleotide binding geometry in this complex explains the previous biochemical analyses of the eukaryotic primase. Based on the complex structure, we constructed a model between the DNA primase and a primer/template DNA for the primer synthesis. This model facilitates the comprehension of the reported features of DNA primase.