What is a defining feature of nuclear receptors?

A defining feature of nuclear receptors is their ability to modulate gene expression through DNA binding. These receptors are a class of proteins found within cells that play a crucial role in cellular communication and regulation. When specific ligands, such as hormones or other signaling molecules, bind to them, nuclear receptors undergo a conformational change that allows them to interact with specific DNA sequences, known as responsive elements.

This interaction leads to the initiation of transcription processes, where RNA polymerase and other transcription factors are recruited to enhance or inhibit the expression of target genes. As a result, nuclear receptors are central to regulating various physiological processes, including development, metabolism, and homeostasis.

Other options, such as the presence of nuclear receptors on the cell surface or their activation by neurotransmitters or ionic influxes, do not accurately describe their fundamental characteristics or mechanisms of action. Instead, nuclear receptors function primarily within the cell's nucleus, interacting with DNA and managing the transcriptional activity of genes in response to specific signaling molecules.