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Molecular and Cellular Biology, August 2008, p. 4734-4744, Vol. 28, No. 15
0270-7306/08/$08.00+0 doi:10.1128/MCB.00588-08
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Department of Biochemistry and Microbiology and The Center for Biomedical Research, University of Victoria, Victoria, BC, Canada V8W 3P6
Received 10 April 2008/ Returned for modification 1 May 2008/ Accepted 22 May 2008
The ability of the MBD4 glycosylase to excise a mismatched base from DNA has been assessed in vitro using DNA substrates with different extents of cytosine methylation, in the presence or absence of reconstituted nucleosomes. Despite the enhanced ability of MBD4 to bind to methylated cytosines, the efficiency of its glycosylase activity on T/G mismatches was slightly dependent on the extent of methylation of the DNA substrate. The reduction in activity caused by competitor DNA was likewise unaffected by the methylation status of the substrate or the competitor. Our results also show that MBD4 efficiently processed T/G mismatches within the nucleosome. Furthermore, the glycolytic activity of the enzyme was not affected by the positioning of the mismatch within the nucleosome. However, histone hyperacetylation facilitated the efficiency with which the bases were excised from the nucleosome templates, irrespective of the position of the mismatch relative to the pseudodyad axis of symmetry of the nucleosome.
Published ahead of print on 2 June 2008.
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