Transcriptional repression by methylation: cooperativity between a CpG cluster in the promoter and remote CpG‐rich regions

摘要: Cytosine methylation of binding sites for transcription factors is a straightforward mechanism to prevent transcription, while data on an indirect mechanism, by outside the factor sites, are still scarce. We have studied latter effect using model promoter construct. For this, 69 bp G + C rich DNA segment with cluster 14 CpG was inserted between upstream lexA and TATA box. Transcription measured in transient transfection assays lexA-VP16 as activating factor. When entire plasmid methylated at all CpGs before transfection, blocked (to 3% residual activity), whereas only mildly inhibited 60%) control that lacked cluster. However, could not simply be attributed cluster: neither otherwise methylation-free reporter gene plasmid, nor unmethylated cluster, considerably (69% 44% remaining activity, respectively). The presented here suggest minimal length required repression, imply concomitant region remote sequences can cooperatively block without need methylate any factors. also note cooperation negative described bears analogy transcriptional activation, where often cooperates enhancer.