Functional conservation of β-hairpin DNA binding domains in the mcm protein of Methanobacterium thermoautotrophicum and the mcm5 protein of Saccharomyces cerevisiae

Mcm proteins are an important family of evolutionarily conserved helicases required for DNA replication in eukaryotes. The eukaryotic Mcm complex of Six paralogs that form a heterohexameric ring. Because the intact. Mcm2-7 hexamer is inactive in vitro, it has been difficult to determine the precis-c function of the different subunits. The solved atomic structure of an archaeal minichromosome maintenance (MCM) homolog provides insight into the function of eukaryotic Mcm proteins. The N-terminal positively charged Central channel in the archaeal molecule consists of beta-hairpin domains essential for DNA binding in vitro. Eukaryotic Mcm proteins also have beta-hairpin domains, but their functions is un-known. With the archaeal atomic structure as a guide, yeast molecular genetics was used to query the functions of the beta-hairpin domains in vivo. A Yeast mcm5 mutant with beta-hairpin mutations displays defects ill the G1/S transition of the cell cycle, the initiation phase of DNA replication, and in the binding of the entire Mcm2-7 complex to replication origins. A similar mcm4 mutation is synthetically lethal with the mcm5 mutation. Therefore, in addition to its known regulatory role, Mcm5 protein has a positive role in origin binding, which requires coordination by all six subunits in the hexamer.