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Molecular and Cellular Biology, October 2008, p. 5865-5873, Vol. 28, No. 19
0270-7306/08/$08.00+0     doi:10.1128/MCB.00161-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Subunit Organization of Mcm2-7 and the Unequal Role of Active Sites in ATP Hydrolysis and Viability{triangledown} ,{dagger}

Matthew L. Bochman,1 Stephen P. Bell,2 and Anthony Schwacha1,2*

Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260,1 Howard Hughes Medical Institute, Department of Biology, Massachusetts Institute of Technology, Cambridge, Massachusetts 021392

Received 30 January 2008/ Returned for modification 5 March 2008/ Accepted 22 July 2008

The Mcm2-7 (minichromosome maintenance) complex is a toroidal AAA+ ATPase and the putative eukaryotic replicative helicase. Unlike a typical homohexameric helicase, Mcm2-7 contains six distinct, essential, and evolutionarily conserved subunits. Precedence to other AAA+ proteins suggests that Mcm ATPase active sites are formed combinatorially, with Walker A and B motifs contributed by one subunit and a catalytically essential arginine (arginine finger) contributed by the adjacent subunit. To test this prediction, we used copurification experiments to identify five distinct and stable Mcm dimer combinations as potential active sites; these subunit associations predict the architecture of the Mcm2-7 complex. Through the use of mutant subunits, we establish that at least three sites are active for ATP hydrolysis and have a canonical AAA+ configuration. In isolation, these five active-site dimers have a wide range of ATPase activities. Using Walker B and arginine finger mutations in defined Mcm subunits, we demonstrate that these sites similarly make differential contributions toward viability and ATP hydrolysis within the intact hexamer. Our conclusions predict a structural discontinuity between Mcm2 and Mcm5 and demonstrate that in contrast to other hexameric helicases, the six Mcm2-7 active sites are functionally distinct.

* Corresponding author. Mailing address: University of Pittsburgh, 4249 Fifth Avenue, 560 Crawford Hall, Pittsburgh, PA 15260. Phone: (412) 624-4307. Fax: (412) 624-4759. E-mail: schwacha{at}pitt.edu

{triangledown} Published ahead of print on 28 July 2008.

{dagger} Supplemental material for this article may be found at http://mcb.asm.org/.

Molecular and Cellular Biology, October 2008, p. 5865-5873, Vol. 28, No. 19
0270-7306/08/$08.00+0     doi:10.1128/MCB.00161-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Snyder, M., Huang, X.-Y., Zhang, J. J. (2009). The Minichromosome Maintenance Proteins 2-7 (MCM2-7) Are Necessary for RNA Polymerase II (Pol II)-mediated Transcription. J. Biol. Chem. 284: 13466-13472 [Abstract] [Full Text]  


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