Cryptocephal, the Drosophila melanogaster ATF4, Is a Specific Coactivator for Ecdysone Receptor Isoform B2
(A) In yeast two-hybrid assays, activation of a UAS-lacZ reporter (reporter activity) required the presence of both EcR-B2 and CRC-A. This interaction was abolished by the EcR-B2 mutation E9K. In these assays, a fusion of the GAL4 DNA-binding domain to either the 17-residue AF1 domain of EcR-B2 (black bars), or the same fragment containing the mutation E9K (gray bars) served as bait. Full length CRC-A was used as the prey. Error bars indicate standard deviations for 4 independent assays. (B) The indicated CRC residues were substituted for full-length CRC-A and tested for binding to the wild-type EcR-B2 fusion fragment in yeast two-hybrid assays. Coordinates of the conserved domains of CRC are indicated in the drawing below.