General transcriptional silencing by a Polycomb response element inDrosophila

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Abstract
Polycomb response elements (PREs) are cis-regulatory sequences required for Polycomb repression of Hox genes in Drosophila. PREs function as potent silencers in the context of Hox reporter genes and they have been shown to partially repress a linked miniwhite reporter gene. The silencing capacity of PREs has not been systematically tested and, therefore, it has remained unclear whether only specific enhancers and promoters can respond to Polycomb silencing. Here, using a reporter gene assay in imaginal discs, we show that a PRE from the Drosophila Hox gene Ultrabithorax potently silences different heterologous enhancers and promoters that are normally not subject to Polycomb repression. Silencing of these reporter genes is abolished in PcG mutants and excision of the PRE from the reporter gene during development results in loss of silencing within one cell generation. Together, these results suggest that PREs function as general silencer elements through which PcG proteins mediate transcriptional repression.