FIG. 3.
Comparison of histone H3 phosphorylation in wild-type (A and B) versus twsP (C and D) mutant larvae. Wild-type and mutant larvae were heat shocked for 0 min (not heat shocked) (A and C) or 10 min (B and D). Polytene chromosomes were prepared and immunostained for Ser10-phosphorylated histone H3 (FITC, yellow) and counterstained with DAPI (white) to view the DNA. Merged images are a composite of both channels shown, with antibody staining (FITC) in yellow and DAPI counterstaining in blue. Prominent ecdysone gene-containing loci are marked in non-heat-shocked chromosomal spreads (A and C). In heat-shocked samples, visible heat shock loci are labeled, and asterisks indicate regions of strong labeling that do not contain heat shock genes (B and D). After a 10-min heat shock, puffing and phosphorylation are observed only at the heat shock loci in wild-type larvae (B). By contrast, numerous loci that do not contain heat shock genes are phosphorylated in twsP mutants during heat shock (D).