Immunoreactive helix-destabilizing protein localized in transcriptionally active regions of Drosophila polytene chromosomes.

A highly purified helix-destabilizing protein (HDP) obtained from rat liver has been used to elicit specific, high-titer anti-HDP sera in rabbits. These antisera show immunological crossreaction with single-stranded DNA binding proteins from several very diverse eukaryotic sources, including Drosophila embryos. The use of such antisera in the labeling of Drosophila salivary gland chromosomes by indirect immunofluorescence shows concentrations of immunoreactive HDP in many regions, but especially in chromosome puffs. There is a striking localization of HDP in heat shock puffs known to be sites of new transcription. The pattern of HDP distribution seems to implicate a transcriptional role, with some specificities independent of puffing itself.