Myc targets of activation are methylated at both H3K4 and H3K27. (A) (Left) A graph showing basal levels of 680 Myc activated targets (blue, left bar, each gene is represented by a thin line) followed by their levels upon ectopic Myc activation (blue, right bar, same genes as in the left bar). (Right) Basal levels of 57 Myc repression targets are shown (red, left bar, each gene is represented by a single thin line), and their levels following the activation of ectopic Myc (red, right bar, same genes as in the left bar). Compare basal levels of the activation targets versus repression targets. (B) Myc activation targets that are also regulated by Pc, Pho and Ash1 are methylated at both H3K4 and H3K27. DNA purified from chromatin immunoprecipitation reactions provided the template for PCR of CG16712 (upper) and CG18108 (lower), and the ChIP antibodies used are indicated above each lane. The right two lanes show results from sequential ChIP of chromatin by one antibody and then another. Input chromatin DNA is shown the far left lane, used in a 1:1000 dilution. (C) The enrichment by IP of chromatin containing 6 genes was calculated by dividing the levels of PCR product by that of the background, no antibody control. CG16712, aTub67C and fs(1)N are all Myc induced, Pc, Ash1 and Pho repressed, and show methylation of H3K4 and K3K27 together. Atg8a is not affected by any of the four regulators, though it is highly expressed in the embryo and methylated at H3K4 (blue bar). Cyp309a1 and CG18108 are Myc/Pc repressed, and show both H3K4 and H3K27 methylation in wild type embryos, but not at the same locus by sequential ChIP. (D) A target of activation by Myc is depicted, with low levels of expression, in a domain of chromatin bearing H3K27 methylation and H3K4 methylation. A growth signal or other signal, including increased Myc accumulation, allows Myc/Max to bind to a binding site, recruiting activators and inducing transcription. Ash1 is shown directly or indirectly repelling PcG repression and maintaining an active H3K4 methylation state. (E) A target of Myc repression is depicted, with high levels of expression mediated by an unknown transcription factor (TF). A cellular signal and increased Myc accumulation allow Pho and Pc required repression, propagating a repressed chromatin state characterized by H3K27 methylation.