Gene transcription is the first and most fundamental step in expressing genetic information, driving critical processes such as embryonic development and cellular responses to stress. Dysregulation of transcription is a hallmark of many diseases, including cancer and neurodegenerative disorders. My research focuses on understanding the structure and function of macromolecular complexes that play pivotal roles in regulating eukaryotic gene transcription. In my talk, I will present our recent structural discoveries, highlighting novel regulatory mechanisms of the transcriptional Mediator complex and uncovering the role of a large intrinsically disordered region in regulating RNA polymerase II-dependent transcription. Additionally, I will discuss the crosstalk between circadian rhythms and hypoxia signaling, with a focus on two key transcription factors. By unraveling these mechanisms, our work not only advances our understanding of fundamental biological processes but also opens new avenues for therapeutic strategies targeting gene expression.