Two orphans find a home

摘要

The superfamily of ligand-regulated transcription factors has grown to the point where the founding members— the steroid and thyroid hormone receptors — have become respected elders. To qualify for membership in this family, all that a protein needs is some homology to the DNA-binding or ligand-binding domains (or both) of a seasoned member. Being a transcription factor or, at least, being able to bind canonical DNA sequence elements is a plus, but being a receptor for a known ligand is not a requirement. As a result, most members are considered 'orphan' nuclear receptors, waiting to be adopted by a ligand. Finding parents, assuming there are any at all, has been tedious and rarely successful. But, on page 612 of this issue, Forman and colleagues report such a success story with several unexpected twists.