FIG. 5.
Sites that contain Ser10-phosphorylated histone H3 isoform also contain active RNA polymerase II during heat shock. Polytene chromosomes were prepared from wild-type (A) and twsP mutant (B) larvae. In addition, salivary glands from wild-type larvae were treated with 50 nM okadaic acid (C). All samples were heat shocked for 20 min at 37°C, immunostained with antibodies against hyperphosphorylated RNA Pol II (Pol IIo, red) and the Ser10-phosphorylated histone H3 isoform (phospho-H3, green), and counterstained with DAPI (white) to view the DNA. DAPI counterstain information is represented as blue in merged images. Visible heat shock gene-containing loci are labeled in all panels. The active form of RNA polymerase II was observed at all sites containing the Ser10-phosphorylated H3 isoform, including the heat shock gene loci (A,B, and C). Additionally, prominent Pol IIo labeling was detected at regions that do not contain heat shock genes (indicated with asterisks) in twsP mutant (B) and okadaic acid-treated (C) chromosomes.