The E75 gene of Manduca sexta and comparison with its Drosophila homolog

The ecdysone-inducible E75 gene responsible for the 75B puff of Drosophila melanogaster encodes a family of proteins which are members of the steroid receptor superfamily. These proteins are believed to be involved in the regulation of ecdysone response. In order to investigate the evolutionary conservation of E75, we have identified the E75 gene of Manduca sexta. We show here the structure of a cDNA believed to encode the Manduca homolog of the E75B protein, and demonstrate that the putative DNA binding, hormone binding and amino and carboxy terminal flanking domains are conserved. However, due to a relative reduction in intron size and number and the absence of homopolymeric amino acid repeats, the E75 B transcription unit and protein are considerably smaller in M. sexta than in D. melanogaster. These findings have implications for the identification of critical structural features of E75 and also suggest that E75 has a conserved function and a shared ligand in Lepidoptera.