Med26 localizes to active genes on polytene chromosomes. (A to F) Untreated polytene chromosomes (A to C) or heat-shocked polytene chromosomes (D to F) stained with Med26 (A, D), Ser5-phosphorylated RNA polymerase II (B, E), and 4′,6-diamidino-2-phenylindole (DAPI), showing DNA with developmental puffs (62A, 4A, 33A, 51D, and 57B in panel C) or HSP loci (63B, 67B, 87A, 87C, 95B, and 93D in panel F) and chromocenter (Het) indicated (C, F). (G to I) Heat-shocked polytene chromosomes stained with Med26 (G), Med17 (H), and DAPI-stained DNA with HSP70 loci (87A, 87C) and P elements bearing only HSEs indicated (I). (J) Diagram of the heat shock protein genes at 87A, 87C, and 67B. (K) qPCR analysis of chromatin precipitated with Med26 antisera under non-heat shock (NHS) or heat shock (HS) conditions. (L) Heat shock protein (Hsp) mRNA expression normalized to Rp49. Mock, mock-treated cells; Med26 RNAi, Med26-depleted cells; Med17 RNAi, Med17-depleted cells. The mRNA level relative to Rp49 is indicated on the y axis.