INTERSPECIFIC TRANSGENIC ANALYSIS OF BASAL VERSUS HEAT-SHOCK-INDUCED EXPRESSION OF A DROSOPHILA-PSEUDOOBSCURA HSP82-NEO FUSION GENE IN DROSOPHILA-MELANOGASTER

Drosophila melanogaster transformants containing a D. pseudoobscura hs p82-neo fusion gene were used to examine the relationship between chro mosome structure and its variation to transcriptional activation and g ene expression. At normal temperatures (25 degrees C) transgenic hsp82 -neo was transcribed in diffuse polytene chromosomal bands encoding an tibiotic G418-resistance without intensive puff formation. Substantial basal expression of the transgene was observed in all tissues examine d: salivary glands, brain, ventral ganglion, foregut, gastric caeca, m idgut, imaginal discs, nurse cells and oo-cytes. In addition, basal hs p82-neo expression occurred throughout embryogenesis. In third-instar larvae subjected to optimal heat shock (36 degrees C), novel heat-shoc k puffs at the transgene insertion sites in polytene salivary gland ch romosomes resulted from a five-fold higher hsp82-neo transcription. Ev en at extreme heat shock (38 degrees C) the transgene puffs correspond ed to transcriptionally active sites. RNA probe protections showed tha t the natural intron of the D. pseudoobscura hsp82-neo transgene was e fficiently removed from pre-mRNA by the D. melanogaster splicing machi nery at 25-36 degrees C. Upon extreme heal shock above 37 degrees C in tron splicing was inhibited. During recovery (25 degrees C) from heat shock (36 degrees C/20 min) the heat-induced hsp82-neo transcription w as rapidly repressed and all novel transgene puffs regressed. The basa l level of transcription of hsp82-neo pre-mRNA was restored within 1-2 h. The hsp82-neo mRNA returned to basal level within 3-4 h. Overall, these results demonstrate a conservation of cis-regulatory elements an d trans-regulatory factors which is needed for faithful expression acr oss the species barrier of the D. pseudoobscura hsp82-neo transgene in D. melanogaster.