Localization of ecdysterone on polytene chromosomes of Drosophila melanogaster.

Abstract

Ecdysterone was crosslinked in situ to polytene chromosomes of salivary glands of D. melanogaster by photoactivation. The crosslinked hormone was localized on the chromosomes by indirect immunofluorescence microscopy. At different developmental stages the hormone was detected at different chromosomal loci. These chromosomal sites correspond to ecdysterone-inducible puff sites. The hormone apparently binds directly to chromosomal loci, whose transcription depends on the presence of the hormone. Ecdysterone was also crosslinked to 1 puff site that regresses during larval development. Hormone binding to polytene chromosomes activates transcription at specific loci, and hormone-dependent regression of intermolt puff 68C is mediated by direct binding of ecdysterone. Ecdysterone was not detected on puff sites that are independent of hormone action or in chromosomal interbands. After heat shock, no ecdysterone became crosslinked to polytene chromosomes.