nuclear receptor

A nuclear receptor is a receptor that doubles as a switch on the genome. Picture a control panel for genes: when the right hormone clicks into it, certain genes get turned up or down. The hormone does not act directly on the cell's machinery — it acts by changing which proteins the cell decides to make.

Once a lipophilic hormone binds, the nuclear receptor becomes an active transcription factor. It attaches to specific DNA sequences near target genes and recruits the cell's transcription machinery, increasing or decreasing the production of messenger RNA and, in turn, protein. Receptors for steroids, thyroid hormone, vitamin D, and retinoic acid all work this way.

Because the effect runs through making new protein, nuclear-receptor signaling is slower to start but produces sustained, often profound changes — controlling growth, metabolism, salt balance, and reproduction. The honest caveat is that the same receptor can switch some genes on while turning others off, depending on the gene and the helper proteins present, so its effects are context-dependent rather than uniform.