Evolution of a New Function by Degenerative Mutation in Cephalochordate Steroid Receptors
A) Full-length BfSR activates transcription of an ERE-driven reporter gene in the presence of 1 µM estradiol (black bars), but activation is inhibited by transfection of increasing quantities of BfER. The quantity of each plasmid transfected is indicated in ng/well. White bars, vehicle-only (no hormone) control. B) Neither BfER nor BfSR activates reporter transcription from an SRE binding site. Cells were transfected with an SRE-driven luciferase reporter and full-length BfER, BfSR, empty vector (pcDNA3), or positive control (HsGR; human GR). Black bars, hormone treatment at 1 uM; white bars, vehicle only.