Chapter 32: Gene Expression Control in Eukaryotes

Key regulatory proteins known as transcription factors are examined, specifically their modular structure containing DNA-binding motifs—such as homeodomains, basic-leucine zippers (bZip), and zinc-finger domains—and activation domains that interact with the Mediator complex and RNA polymerase II,. The text explains the critical role of enhancers, which can regulate gene activity from distant locations on the chromosome, and how combinatorial control allows for the differentiation of distinct cell types, including the generation of induced pluripotent stem (iPS) cells using specific factors,. Significant attention is devoted to epigenetics and chromatin remodeling, including the methylation of cytosines in CpG islands which typically correlates with gene repression, and the "histone code" involving covalent modifications like acetylation,. The mechanism of nuclear hormone receptors is detailed, illustrating how steroid hormones like estrogen bind to receptors to recruit coactivators and histone acetyltransferases (HATs), and how drugs like tamoxifen function as antagonists or selective estrogen receptor modulators (SERMs) in cancer treatment,. The summary further describes how bromodomains within chromatin-remodeling complexes recognize acetylated histones to facilitate transcription. Finally, the chapter covers posttranscriptional regulation, using the control of iron metabolism via iron-response elements (IREs) and cytosolic aconitase (IRP) as a primary example, alongside the widespread gene-silencing role of microRNAs (miRNAs) and the Argonaute family in the RNA interference pathway.