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

A 10 or 20 min in vitro treatment of salivary glands of late 3rd instar larvae of Drosophila melanogaster with 1 mg/ml benzamide (BM) at 24 degrees C results in the specific induction of the 93D 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 degrees 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 93D 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 degrees C) incorporation on all TS puffs is relatively less and significantly, in both cases, the 87C puff is much less active active (more so in TS followed by BM treated glands) than the 87A puff. Also, in both these treatments, the 93D puff does not show ant additive effect on the BM and TS treatments. These observations are discussed in the light of possible role of the 93D puff in modulating the heat shock response.