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Molecular and Cellular Biology, April 2007, p. 3044-3055, Vol. 27, No. 8
0270-7306/07/$08.00+0     doi:10.1128/MCB.02384-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Identification and Characterization of a Novel Component of the Human Minichromosome Maintenance Complex{triangledown}

Amos M. Sakwe,{dagger} Tin Nguyen,{dagger} Vicki Athanasopoulos, Kathy Shire, and Lori Frappier*

Department of Medical Genetics and Microbiology, University of Toronto, Toronto, Canada

Received 20 December 2006/ Returned for modification 18 January 2007/ Accepted 1 February 2007

Minichromosome maintenance (MCM) complex replicative helicase complexes play essential roles in DNA replication in all eukaryotes. Using a tandem affinity purification-tagging approach in human cells, we discovered a form of the MCM complex that contains a previously unstudied protein, MCM binding protein (MCM-BP). MCM-BP is conserved in multicellular eukaryotes and shares limited homology with MCM proteins. MCM-BP formed a complex with MCM3 to MCM7, which excluded MCM2; and, conversely, hexameric complexes of MCM2 to MCM7 lacked MCM-BP, indicating that MCM-BP can replace MCM2 in the MCM complex. MCM-BP-containing complexes exhibited increased stability under experimental conditions relative to those containing MCM2. MCM-BP also formed a complex with the MCM4/6/7 core helicase in vitro, but, unlike MCM2, did not inhibit this helicase activity. A proportion of MCM-BP bound to cellular chromatin in a cell cycle-dependent manner typical of MCM proteins, and, like other MCM subunits, preferentially associated with a cellular origin in G1 but not in S phase. In addition, down-regulation of MCM-BP decreased the association of MCM4 with chromatin, and the chromatin association of MCM-BP was at least partially dependent on MCM4 and cdc6. The results indicate that multicellular eukaryotes contain two types of hexameric MCM complexes with unique properties and functions.

* Corresponding author. Mailing address: 1 Kings College Circle, Toronto, Ontario, Canada M5S 1A8. Phone: (416) 946-3501. Fax: (416) 978-6885. E-mail: lori.frappier{at}utoronto.ca

{triangledown} Published ahead of print on 12 February 2007.

{dagger} A.M.S. and T.N. contributed equally to this work.

Molecular and Cellular Biology, April 2007, p. 3044-3055, Vol. 27, No. 8
0270-7306/07/$08.00+0     doi:10.1128/MCB.02384-06
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



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