Abstract
The ring-shaped MCM helicase is essential to all phases of DNA replication. The complex loads at replication origins as an inactive double-hexamer encircling duplex DNA. Helicase activation converts this species to two active single hexamers that encircle single-stranded DNA (ssDNA). The molecular details of MCM DNA interactions during these events are unknown. We determined the crystal structure of the Pyrococcus furiosus MCM N-terminal domain hexamer bound to ssDNA and define a conserved MCM-ssDNA binding motif (MSSB). Intriguingly, ssDNA binds the MCM ring interior perpendicular to the central channel with defined polarity. In eukaryotes, the MSSB is conserved in several Mcm2-7 subunits, and MSSB mutant combinations in S. cerevisiae Mcm2-7 are not viable. Mutant Mcm2-7 complexes assemble and are recruited to replication origins, but are defective in helicase loading and activation. Our findings identify an important MCM-ssDNA interaction and suggest it functions during helicase activation to select the strand for translocation. DOI: http://dx.doi.org/10.7554/eLife.01993.001.
Highlights
Mcm proteins were first identified in yeast when mutations in their genes were defective for minichromosome maintenance (Maiorano et al, 2006)
To elucidate how MCM interacts with singlestranded DNA (ssDNA), we determined the crystal structure of the N-terminal domain of the Pyrococcus furiosus MCM (PfMCMN) protein in complex with homopolymeric30 ssDNA (Table 1)
We show how the PfMCM N-terminal domain interacts with single-stranded DNA and identify a critical set of interacting residues that we define as the MSSB
Summary
Mcm proteins were first identified in yeast when mutations in their genes were defective for minichromosome maintenance (Maiorano et al, 2006). To investigate the interactions after origin melting and how the MCM hexamer selectively encircles the leading strand template, we determined the crystal structure of the MCMN hexamer of Pyrococcus furiosus bound to ssDNA. Our findings support a model in which the identified MCM-ssDNA interactions contribute to the selection of the leading strand DNA template during helicase activation.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
