Nucleic Acids Research Advance Access published online on May 27, 2009
Nucleic Acids Research, doi:10.1093/nar/gkp376
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Nucleic Acid Enzymes |
A biochemically active MCM-like helicase in Bacillus cereus
1Department of Molecular and Cellular Biology, Harvard University, 7 Divinity Avenue, Cambridge, MA 02138, 2Center for Advanced Research in Biotechnology, University of Maryland Biotechnology Institute, 9600 Gudelsky Drive, Rockville, MD 20850, 3Laboratory of Mass Spectrometry and Gaseous Ion Chemistry, The Rockefeller University, 1230 York Avenue, NY 10065 and 4Analytical Chemistry Division, National Institute of Standards and Technology, 100 Bureau Drive, Gaithersburg, MD 20899-8391, USA
*To whom correspondence should be addressed. Tel: +1 617 496 9734; Fax: +1 617 496 9684; Email: dj{at}mcb.harvard.edu
Present address: Jae-Ho Shin, School of Applied Biosciences, Kyungpook National University, Daegu 702-701, Republic of Korea.
Received January 23, 2009. Revised April 13, 2009. Accepted April 26, 2009.
The mini-chromosome maintenance (MCM) proteins serve as the replicative helicases in archaea and eukaryotes. Interestingly, an MCM homolog was identified, by BLAST analysis, within a phage integrated in the bacterium Bacillus cereus (Bc). BcMCM is only related to the AAA region of MCM-helicases; the typical amino-terminus is missing and is replaced by a segment with weak homology to primases. We show that BcMCM displays 3'
5' helicase and ssDNA-stimulated ATPase activity, properties that arise from its conserved AAA domain. Isolated BcMCM is a monomer in solution but likely forms the functional oligomer in vivo. We found that the BcMCM amino-terminus can bind ssDNA and harbors a zinc atom, both hallmarks of the typical MCM amino-terminus. No BcMCM-catalyzed primase activity could be detected. We propose that the divergent amino-terminus of BcMCM is a paralog of the corresponding region of MCM-helicases. A divergent amino terminus makes BcMCM a useful model for typical MCM-helicases since it accomplishes the same function using an apparently unrelated structure.