Chromosoma (Berl) (1986) 94:273 278 CHROMOSOMA 9 Springer-Verlag1986 Expression of 93D heat shock puff of Drosophila melanogaster in deficiency genotypes and its influence on activity of the 87C puff Pradeep Kumar Burma and S.C. Lakhotia Cytogenetics Laboratory, Department of Zoology, Banaras Hindu University, Varanasi 221 005, India Abstract. Using the overlapping deficiencies Df(3R)GC14 and Df(3R)e ~p4 of the 93D region of Drosophila melano- gaster, the benzamide (BM)-inducible site in polytene chromsomes was localised to the 93D6-7 region, which had earlier been identified as heat inducible. The normal devel- opmental and BM-induced 93D6-7 puff was found to be dosage compensated since in larvae heterozygotus for a defi- ciency, with one dose of 93D6-7, the rate of 3H-uridine incorporation in this puff was the same as in the wild type with two doses. Curiously, however, heat shock (37 ~ C) caused regression of the 93D6-7 puff on the normal chro- mosome in heterozygotes. In agreement with earlier results from our laboratory, the non-inducibility of the single-dose 93D locus by heat shock in the heterozygotes, caused the 87C puff to be nearly half as active as the 87A puff at 37 ~ C. However, in eGp4/GC14 larvae, lacking the 93D6-7 locus on both homologues, the 87C puff was less active than 87A in some heat-shocked larvae but in other larvae 87A and 87C were equally active. Possible reasons for this inter-larval variability are discussed. Introduction The major heat shock puff at 93D in Drosophila melano- gaster has several distinctive features. It can be specifically induced by agents like benzamide (Lakhotia and Mukherjee 1980) and colchicine (Lakhotia and Mukherjee 1984) and apparently has no translational product (Lakhotia and Mukherjee 1982), although a deletion of this locus affects the viability of the fly (Mohler and Pardue 1984). An equiv- alent of the 93D locus seems to be a component of the heat shock response in every Drosophila species studied (Lakhotia and Singh 1982). The 93D heat shock site has been mapped cytologically between the distal breakpoint of Df(3R)e ~p4 and the prox- imal breakpoint of Df(3R)GC14, i.e. in the 93D6 7 region of 3R (Mohler and Pardue 1982). Bearing in mind that 93D is also specifically induced by benzamide (Lakhotia and Mukherjee 1980) we used the overlapping deficiencies e Gp* and GC14 (Mohler and Pardue 1982) to test whether the benzamide trancription site corresponds cytologically to the heat shock trancription site. Earlier observations in our laboratory had shown that Offprint requests to: S.C. Lakhotia any perturbation during heat shock that led to a regression of the 93D puff also resulted in unequal expression of the duplicate heat shock loci at 87A and 87C which are other- wise induced equally by heat shock (Lakhotia and Mukher- jee 1980, 1984; Lakhotia and Singh 1985, Mukherjee and Lakhotia 1982). The availability of the overlapping defi- ciencies allowed an examination of the response of the 87A and 87C loci to heat shock in the absence of 93D locus. Our results showed that in the genotoype deficient for 93D, the 87C locus was indeed less active than 87A. They also revealed that in heterozygotes, with only one dose of the 93D locus, the normal developmental as well as benzamide- induced activity was dosage compensated. However, it is intriguing that in response to heat shock the 93D locus in the heterozygotes which is normally hyperactive for dos- age compensation, regressed completely, rather than be- coming more active. Materials and methods Strains. Wild-type (Oregon R +) and mutant stocks carrying deficiencies of parts of the right arm of chromosome 3 of Drosophila melanogaster were used for these studies. The deficiency stocks were Df(3R) GC14/TM6B and Df(3R)eGp4/TM6B (described by Mohler and Pardue 1982, 1984). In Df(3R)GC14 the deficiency spans from 93D6-7 to 93D10 while Df(3R)e Gp4, lacks 93Bl1-13 to 93D6-7. These two stocks along with the wild-type stock of D. mel- anogaster were use to generate larvae homozygously and het- erozygously deficient for the 93D6-7 bands which harbour the heat shock locus (Mohler and Pardue 1982). The crosses used to generate such larvae are summarised in Table 1. Culture conditions. All Drosophila stocks and progeny lar- vae were grown on standard medium containing agar, corn- meal, brown sugar and yeast at 20~ 1~ C. Eggs were col- lected at hourly intervals in food-filled Petri dishes. Larval cultures were provided with additional yeast suspension for healthy growth. Treatments. Freshly excised salivary glands from actively migrating late third instar larvae of different genotypes (Ta- ble 1) were used for the different treatments. The medium used for dissection and incubation of glands for the treat- ments was as described earlier (Lakhotia and Mukherjee 1980). For heat shock (HS), sister salivary glands from dif-