Negative and positive effects of CpG-methylation on Xenopus ribosomal gene transcription in vitro.
Methylation of cytosine-residues in the sequence CpG affects the expression of many genes and generally correlates with reduced transcription. The ribosomal genes of Xenopus laevis were among the first genes to be studied with respect to their DNA methylation, and a loss of methylation during embryonic development correlated with the onset of transcription. Nevertheless, highly methylated ribosomal genes were transcribed at normal levels when injected into oocyte nuclei, and thus transcription of these genes was generally assumed to be insensitive to CpG-methylation. Here I show that Xenopus ribosomal gene transcription can be repressed by cellular factors binding to meCpG, similarly as it has been described for transcription by RNA polymerase II. In the absence of these repressors, however, CpG-methylation has a direct positive effect on RNA polymerase I-promoter activity.
Labhart
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Scripps Research Institute, Department of Molecular and Experimental Medicine, La Jolla, CA 92037.
D000818:Animals; D004275:DNA, Ribosomal / Q000378:metabolism*; D015226:Dinucleoside Phosphates; D008745:Methylation; D010957:Plasmids; D011401:Promoter Regions, Genetic; D012045:Regulatory Sequences, Nucleic Acid; D015183:Restriction Mapping; D012270:Ribosomes / Q000378:metabolism*; D013698:Templates, Genetic; D013728:Terminator Regions, Genetic; D014158:Transcription, Genetic; D014982:Xenopus laevis
D004275:DNA, Ribosomal; D015226:Dinucleoside Phosphates; C015772:CpG dinucleotide