Final answer:
Hormone response elements (HREs) are specific DNA sequences that interact with steroid hormone receptors to regulate gene expression. Once a hormone binds to its receptor, the complex can act as a transcription factor, influencing whether a gene is turned on or off. This mechanism facilitates vital cellular functions and organismal responses to hormonal signals.
Step-by-step explanation:
Hormone response elements (HREs) are critical components in the regulation of gene expression by hormones. These elements are specific DNA sequences located within the promoter region of a gene. When steroid hormone receptors bind to their respective hormones, they undergo a conformational change allowing them to bind to the HRE. This binding, in turn, can activate or repress the transcription of the target gene, which is an essential process for regulating cellular function.
For example, the glucocorticoid receptor is a type of steroid hormone receptor that, once bound to its hormone, can recognize and bind to the glucocorticoid response element - a palindromic DNA sequence. The receptor, functioning as a transcription factor equipped with zinc-finger domains, can influence the transcription of genes involved in a multitude of cellular responses. This can result in the production of protein products necessary for cell function and stress response.
Intracellular nuclear receptors, such as those for glucocorticoids, begin in the cytoplasm attached to a heat shock protein (HSP). Upon hormone binding, these receptors are released from the HSP and move to the nucleus where they interact with HREs to modulate gene transcription. This mechanism of action underlies the ability of steroid hormones to elicit changes in cellular activity affecting the entire organism.