FIG. 1.

Effect of okadaic acid on histone H3 phosphorylation during heat shock. Salivary glands isolated from wild-type larvae were incubated in Grace's medium containing 0 nM (A), 10 nM (B), 50 nM (C), and 100 nM (D) okadaic acid. All salivary glands were heat shocked at 37°C for 20 min before squashing, immunostained for Ser10-phosphorylated histone H3 (FITC, yellow), and counterstained with DAPI (white). Merged images are a composite of both channels shown, antibody staining in yellow and DAPI counterstaining in blue. In all photographs, identifiable heat shock loci are labeled; although not all heat shock genes are visible in these photographs, data shown in other figures indicate that all contain Ser10-phosphorylated histone H3. Comparison of treated with untreated chromosomes indicates that okadaic acid prevents the genome-wide dephosphorylation of Ser10-phosphorylated histone H3 isoforms during heat shock.