Identification of a heat shock locus by whole mount electron microscopy of polytene chromosomes

Abstract

The suitability of whole mount electron microscopy for the localization of gene activity in polytene chromosomes was tested by heat shock induction in Drosophila hydei. The heat shock response of salivary glands is found out to be detrimental to surface spreading properties of salivary gland material. The major heat shock band in division 81 is determined to be 81C2. The heat shock puff is covered by amorphous material probably representing transcription complexes that partly obscure the underlying structures. After 5 min heat shock treatment, spherical particles are observed on the puff site. Successful mapping of this region, which consists of very thin bands including a developmental puff, suggests that whole mount electron microscopy is the method of choice for routine localization of gene activity in polytene chromosome systems.