Transcriptional repression mediated by polycomb group proteins and other chromatin-associated repressors is selectively blocked by insulators.
Polycomb group (PcG) proteins repress gene activity over a considerable distance, possibly by spreading along the chromatin fiber. Insulators or boundary elements, genetic elements within the chromatin, may serve to terminate the repressing action of PcG proteins. We studied the ability of insulators to block the action of chromatin-associated repressors such as PcG proteins, HP1, and MeCP2. We found that the Drosophila special chromatin structure insulator completely blocks transcriptional repression mediated by all of the repressors we tested. The Drosophila gypsy insulator was able to block the repression mediated by the PcG proteins Su(z)2 and RING1, as well as mHP1, but not the repression mediated by MeCP2 and the PcG protein HPC2. The 5'-located DNase I-hypersensitive site in the chicken beta-globin locus displayed a limited ability to block repression, and a matrix or scaffold attachment region element was entirely unable to block repression mediated by any repressor tested. Our results indicate that insulators can block repression mediated by PcG proteins and other chromatin-associated repressors, but with a high level of selectivity. This high degree of specificity may provide a useful assay to define and characterize distinct classes of insulators.
van der Vlag
J
J
E. C. Slater Instituut, BioCentrum Amsterdam, University of Amsterdam, Plantage Muidergracht 12, 1018 TV Amsterdam, The Netherlands.
den Blaauwen
J L
JL
Sewalt
R G
RG
van Driel
R
R
Otte
A P
AP
D000818:Animals; D002460:Cell Line; D002843:Chromatin / Q000378:metabolism*; D002868:Chromosomal Proteins, Non-Histone / Q000378:metabolism*; D004251:DNA Transposable Elements; D004330:Drosophila / Q000235:genetics; D029721:Drosophila Proteins; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006801:Humans; D019476:Insect Proteins / Q000378:metabolism*; D009698:Nucleoproteins / Q000378:metabolism*; D009707:Nucleosomes / Q000378:metabolism; D063150:Polycomb Repressive Complex 1; D012097:Repressor Proteins / Q000378:metabolism*; D014158:Transcription, Genetic
D002843:Chromatin; D002868:Chromosomal Proteins, Non-Histone; D004251:DNA Transposable Elements; D029721:Drosophila Proteins; D019476:Insect Proteins; D009698:Nucleoproteins; D009707:Nucleosomes; C066770:Pc protein, Drosophila; D012097:Repressor Proteins; D063150:Polycomb Repressive Complex 1