During Drosophila development, Polycomb (PcG) and trithorax (trxG)group proteins maintain DNA regions in transcriptionally silent and active states, respectively, by forming complexes that modify chromatin. Surprisingly, Fujioka and colleagues now report that the DNA-binding PcG protein Pleiohomeotic (Pho) maintains both active and repressed transcriptional states of even skipped (eve; a Drosophila gene with a conserved role in the regulation of nervous system gene expression) through a single site (see ). The researchers identify a Pho-dependent sequence at the 3' border of the eve locus. They then show that, while this element maintains repression in nervous system cells in which eve is silenced during early development, it unexpectedly maintains an active transcriptional state in other cells. Both negative and positive transcriptional maintenance depend on Pho binding and on pho gene activity. From these and other results, the researchers suggest that the differential regulation of a core DNA-binding complex that contains Pho and other factors facilitates the transcriptional memory of both active and repressed states during development.
