Specific activation of puff 93D of Drosophila melanogaster by benzamide and the effect of benzamide treatment on the heat shock induced puffing activity

Abstract

A 10 or 20 min in vitro treatment of salivary glands of late 3rd instar larvae of Drosophila melanogaster with l mg/ml benzamide (BM) at 24°C results in the specific induction of the 93 D puff and at the same time all other chromosomal RNA synthesis is severely repressed. Incorporation of 3H-uridine in the nucleolus is not affected. In glands heat shocked (37° C) for 20 min in presence of BM, all the temperature shock (TS) puffs are induced but they incorporate ³H-uridine to a lesser extent than in glands heat shocked in absence of BM. The 93 D puff, which is highly induced by either of the treatments alone, is relatively less active in glands exposed to TS and BM simultaneously. When a 10 min BM treatment (at 24° C) precedes a 20 min TS or when the BM treatment follows TS, the ³H-uridine incorporation on all TS puffs is relatively less and significantly, in both cases, the 87 C puff is much less active (more so in TS followed by BM treated glands) than the 87 A puff. Also, in both these treatments, the 93 D puff does not show any additive effect of the BM and TS treatments. These observations are discussed in the light of possible role of the 93 D puff in modulating the heat shock response.