A severe birth defect syndrome called retinoic acid embryopathy (243440) is caused by medications such as Accutane when taken by pregnant women for treatment of acne. Retinoic acid and steroid hormones are group I signals that cross the cell membrane to interact with cytosolic or nuclear receptors. Which of the structural domains of such receptors would interact with retinoic acid?
1.Transcription activating domains
2.Ligand binding domains
3.DNA-binding domains
4.Response elements
5.Antirepressor domains
Solution:
Mammalian regulatory factors are much more diverse than those of bacteria, possessing several types of structural domains. Activators of transcription, such as steroid hormones, may enter the cell and bind to regulatory factors at specific sites called ligand-binding domains; these intracellular “receptors” are analogous to G protein-linked membrane receptors that extend into the extracellular space. Response elements are not regulatory factors but DNA sequences near the transcription site for certain types of genes (e.g., steroid-responsive and heat shock-responsive genes). Regulatory factors interact with specific DNA sequences through their DNA-binding domains and with other regulatory factors through transcription-activating domains. Some regulatory factors have antirepressor domains that counteract the inhibitory effects of chromatin proteins (histones and nonhistones).