Polycomb Silencing Blocks Transcription Initiation

• Published in: Molecular cell 2004-03, Vol.13 (6), p.887-893
• Main Authors: Dellino, Gaetano I, Schwartz, Yuri B, Farkas, Gabriella, McCabe, Donna, Elgin, Sarah C.R, Pirrotta, Vincenzo
• Format: Article
• Language: English
• Subjects: Animals; Biomarkers; Chromatin - metabolism; DNA Footprinting; DNA Transposable Elements; DNA-Directed RNA Polymerases - metabolism; Drosophila; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; Gene Silencing; Genes, Insect; Heat-Shock Proteins - genetics; Polycomb Repressive Complex 1; Precipitin Tests; Promoter Regions, Genetic; Transcription Factors - metabolism; Transcription, Genetic; Transgenes
• ISSN: 1097-2765; 1097-4164; 1097-4164
• DOI: 10.1016/S1097-2765(04)00128-5

Polycomb (PcG) complexes maintain the silent state of target genes. The mechanism of silencing is not known but has been inferred to involve chromatin packaging to block the access of transcription factors. We have studied the effect of PcG silencing on the hsp26 heat shock promoter. While silencing does decrease the accessibility of some restriction enzyme sites to some extent, it does not prevent the binding of TBP, RNA polymerase, or the heat shock factor to the hsp26 promoter, as shown by chromatin immunoprecipitation. However, we find that in the repressed state, the RNA polymerase cannot initiate transcription. We conclude that, rather than altering chromatin structure to block accessibility, PcG silencing in this construct targets directly the activity of the transcriptional machinery at the promoter.