Overlapping antiparallel transcripts induced by ecdysone in a Drosophila cell line.
Treating Drosophila Kc tissue culture cells with 20-hydroxyecdysone (20E) causes a rapid 10-fold increase in the synthesis of three polypeptides, with molecular weights of 28 kD, 29 kD, and 40 kD (named EIP28, EIP29, and EIP 40, in reference to their molecular weights), as shown by Savakis et al. (1980, 1984). Genomic clones that include Eip40, a gene encoding the EIP40 polypeptide, have been isolated and used to characterize transcription in a 10 kilobase region. At least five different transcripts are produced from this region in Kc cells. One of these transcripts is overlapping and antiparallel to the Eip40 transcript. Although these genes are located quite near one another, their response to 20E varies from little, if any, induction to an induction that is at least 25 fold. Approximately 2.5 kb of DNA which encompasses the Eip40 gene has been sequenced. Analysis of this sequence shows that Eip40 encodes a Drosophila homologue of the enzyme cystathionase. The complementary DNA strand, which produces an 1800 N transcript, has a 645 N open reading frame (ORF). This ORF shows some similarity to cystathionase, the protein encoded by the complementary strand, but shows no detectable similarity to other reported protein sequences.