Induction of a heat shock puff by hypoxia in polytene foot pad chromosomes of Sarcophaga bullata.

Abstract

The single large heat-responsive puff (hs puff) in polytene foot pad cells of fly pupae (Sarcophaga bullata) is shown to be inducible by oxygen deprivation but not, as in other systems, by reoxygenation following an hypoxic treatment. The ambient oxygen concentration must drop below 2% for the hs puff to be maximally induced but the puff is fully inducible and transcriptionally active even in the complete absence of oxygen. Lack of oxygen is also compatible with continued transport of puff materials (formation and dissipation of puff droplets at the hs locus). Hypoxia-induced hs puffs persist indefinitely (greater than 2 days) at maximal or intermediate size and only regress completely after oxygen is resupplied. The induction of the hs puff during hypoxia is highly specific and does not seem to involve activation of any other chromosomal loci, yet the reaction is not confined to the giant foot pad cells or to specific developmental stages. Azide poisoning of cultured foot pads simulates the in vivo effects of hypoxia. The induction of the hs puff by azide, heat, or other means is inhibited by sulfhydryl reagents (iodoacetamide, arsenite) and fluoride, but not by an inhibitor of substrate-linked phosphorylation (arsenate). Instead, arsenate, like other uncouplers (2,4-dinitrophenol) is an inducer of the hs locus. The hs puff can be fully induced by hypoxia at any temperature between 2 degrees and 45 degrees C. The rate of puff expansion is strictly temperature dependent and the temperature characteristics of this process are remarkably similar to those of a promoter RNA polymerase association.(ABSTRACT TRUNCATED AT 250 WORDS)