Flounder antifreeze protein synthesis under heat shock control in transgenic Drosophila melanogaster.

The gene coding for the most abundant antifreeze protein (AFP) in the winter flounder was placed downstream of the Drosophila melanogaster hsp70 promoter and introduced into the D. melanogaster germ line by P-element-mediated transformation. In each of six transgenic strains tested, heat shock treatment induced the expression of two major AFP gene transcripts and one minor one. All three transcripts were spliced despite the lack of an obvious D. melanogaster internal intron-splicing sequence. The variation in transcript length was caused by selection of different polyadenylation sites. Western blots showed the presence of immunoreactive AFP in hemolymph from heat-shocked transformants. The immunoreactive material had a molecular weight of 6,200, which is consistent with the loss of the signal sequence from the primary translation product and the retention of the pro sequence. Thus, all the signals for flounder pre-mRNA and preprotein processing were recognized in D. melanogaster.