Originally published as Genetics Published Articles Ahead of Print on July 27, 2008.

Genetics, Vol. 179, 1757-1768, August 2008, Copyright © 2008
doi:10.1534/genetics.108.088690

Functional Conservation of β-Hairpin DNA Binding Domains in the Mcm Protein of Methanobacterium thermoautotrophicum and the Mcm5 protein of Saccharomyces cerevisiae

Ronald P. Leon*,{dagger},1, Marianne Tecklenburg* and Robert A. Sclafani*,{dagger},2

* Department of Biochemistry and Molecular Genetics and the {dagger} Program in Molecular Biology, School of Medicine, University of Colorado, Denver, Colorado 80045

2 Corresponding author: Department of Biochemistry and Molecular Genetics, P.O. Box 6511, Mail Stop 8101, Bldg. RC-1, Room L18-9100, School of Medicine, University of Colorado, Aurora, CO 80045.
E-mail: robert.sclafani{at}UCHSC.edu

Mcm proteins are an important family of evolutionarily conserved helicases required for DNA replication in eukaryotes. The eukaryotic Mcm complex consists 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 precise 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 β-hairpin domains essential for DNA binding in vitro. Eukaryotic Mcm proteins also have β-hairpin domains, but their function is unknown. With the archaeal atomic structure as a guide, yeast molecular genetics was used to query the function of the β-hairpin domains in vivo. A yeast mcm5 mutant with β-hairpin mutations displays defects in 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 Mcm2-7 subunits in the hexamer.