Structure of the Eip28/29 gene, an ecdysone-inducible gene from Drosophila

The EIPs 28 and 29 are a family of polypeptides identified originally by their ecdysone inducibility in Drosophila cell lines. At least two family members, 28III and 29III, appear to be primary translation products. Here we describe a unique Eip28/29 gene that must encode both primary products. The Eip28/29 gene is unique because the cloned genomic DNA hybridizes to both EIP 28 and 29 messenger RNAs under stringent conditions, but does not anneal detectably to other genomic sequences even under mild conditions. Furthermore the diverse products of this gene are not alleles because flies homozygous for the chromosomal region (71CD) containing the Eip28/29 gene produce mRNAs that translate to yield all the EIPs 28 and 29. We report here the sequence of a 2855-nucleotide region encompassing the Eip28/29 gene. By comparisons with complementary DNA sequences and by nuclease protection experiments we have derived a complete structure for the Eip28/29 transcription unit. The primary transcript is 2146 nucleotides long and is processed by the removal of three introns to yield the predominant mature transcript in tissue culture cells (979 nucleotides). This transcript probably corresponds to the 28III mRNA. Neither the start of the transcription unit nor the structure of the predominant transcript is affected by the hormone ecdysone. The genomic sequence reveals a series of heptanucleotide and octanucleotide repeats of unknown function that fall at about 50-nucleotide intervals within the first 150 nucleotides upstream from the transcription unit. In addition this sequence, when combined with previously published data, suggests that the consensus cap site sequence in Drosophila may be extended to include 13 nucleotides centered on the heptanucleotide core previously recognized by Snyder et al. (1982).