Protein binding protects sites on stable episomes and in the chromosome from de novo methylation.
We have utilized the Escherichia coli lac repressor-operator system to test whether protein binding can interfere with de novo DNA methylation in mammalian cells. We find that a DNA binding protein can protect sites on the episome as well as in the genome from the de novo methylation activity of Dnmt3a. Transcriptional machinery moving through the binding sites does not affect the de novo methylation of these sites, and it does not affect the binding protein protection of these sites from de novo methylation. This study and previous studies provide a possible mechanism for the observation that an Sp1 site can serve as a cis-acting signal for demethylation and for preventing de novo methylation of the CpG island upstream of the mouse adenine phosphoribosyltransferase (Aprt) gene. These findings also support the hypothesis that protein binding may play a crucial role in changes of CpG methylation pattern in mammalian cells.
Han
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Department of Urology and Department of Biochemistry and Molecular Biology, University of Southern California, Los Angeles, California 90033, USA.
Lin
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Hsieh
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D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D004269:DNA, Bacterial / Q000235:genetics / Q000378:metabolism; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins; D015964:Gene Expression Regulation, Bacterial; D056968:Lac Repressors; D010957:Plasmids / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism*
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D029968:Escherichia coli Proteins; D056968:Lac Repressors; C539064:LacI protein, E coli; D012097:Repressor Proteins