Molecular mechanisms mediating methylation-dependent silencing of ribosomal gene transcription.
Epigenetic control mechanisms silence about half of ribosomal RNA genes (rDNA) in metabolically active cells. In the mouse, 40% of rDNA repeats are methylated and can be activated by 5-azacytidine treatment. In exploring the effect of methylation on rDNA transcription, we found that methylation of a single CpG dinucleotide within the upstream control element of the rDNA promoter (at -133) abrogates rDNA transcription both in transfection experiments and in in vitro assays using chromatin templates. Chromatin immunoprecipitation assays demonstrate that methylation of the cytosine at -133 inhibits binding of the transcription factor UBF to nucleosomal rDNA, thereby preventing initiation complex formation. Thus, methylation may be a mechanism to inactivate rDNA genes and propagate transcriptional silencing through cell division.
Santoro
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Division of Molecular Biology of the Cell II, German Cancer Research Center, D-69120 Heidelberg, Germany.
Grummt
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D016475:3T3 Cells; D000818:Animals; D001374:Azacitidine / Q000494:pharmacology; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D018899:CpG Islands / Q000235:genetics; D018983:DNA Footprinting; D019175:DNA Methylation; D004275:DNA, Ribosomal / Q000235:genetics / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D020868:Gene Silencing; D017930:Genes, Reporter / Q000235:genetics; D020459:Genes, rRNA; D051379:Mice; D009687:Nuclear Proteins / Q000378:metabolism; D011233:Precipitin Tests; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors / Q000378:metabolism; D014158:Transcription, Genetic / Q000235:genetics*
D002843:Chromatin; D004275:DNA, Ribosomal; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D009687:Nuclear Proteins; D000074482:Thyroid Nuclear Factor 1; D014157:Transcription Factors; D001374:Azacitidine