The Effect of Heat Shock on Gene Expression in Drosophila melanogaster

When Drosophila melanogasteris exposed to 37~ a series of specific genes is activated, whereas most of the other genes, active at 25 ~ before this heat shock, appear to be repressed. The induction of about eight or nine new puffs on the salivary gland chromosomes occurs very shortly after the temperature shift to 37 ~ and at the same time most of the puffs active at 25 ~ before the heat shock rapidly regress at 37 ~ (Ritossa 1962; Ashburner 1970). The same new puffs are induced under a variety of other stress conditions unrelated to temperature (Berendes 1972; Lewis et al. 1975). The heat shock also induces the rapid synthesis of a small number of proteins, whereas the rate of syn-thesis of most cellular proteins, normally made at 25 ~ is strongly reduced (Tissi~res et al. 1974; Lewis et al. 1975; McKenzie et al. 1975). This phenomenon is observed in different issues (Tissi~res et al. 1974), in many different wild-type strains (L. Moran and A. P. Arrigo, unpubl.), and in different Drosophila rnelanogaster tissue-culture cell lines (McKenzie et