21.5 Steroid receptors have several independent domains Receptor is a transmembrane protein. located in the plasma membrane, that binds a ligand in a domain on the extracellular side. and as a result has a change in activity of the cytoplasmic domain (The same term is sometimes used also for the steroid receptors, which are transcription factors that are activated by binding ligands that are steroids or other small molecules. 消当Receptor is a transmembrane protein, located in the plasma membrane, that binds a ligand in a domain on the extracellular side, and as a result has a change in activity of the cytoplasmic domain. (The same term is sometimes used also for the steroid receptors, which are transcription factors that are activated by binding ligands that are steroids or other small molecules.) 21.5 Steroid receptors have several independent domains