Ribosome structure, function and dysfunction at the molecular level

Ribosomes are essential ribonucleoprotein complexes that translate genetic information into proteins and are therefore central to cellular growth, development, and homeostasis. Recent advances in structural biology and genomics have transformed our understanding of ribosomes from static translational machines to highly dynamic complexes whose assembly, function, and quality control are tightly regulated. In this review, we provide an overview of eukaryotic ribosome structure and biogenesis, focusing on insights gained from yeast and human systems. We discuss the hierarchical assembly of ribosomal subunits, rRNA processing and modification, nuclear export, and cytoplasmic maturation. Particular emphasis is placed on the surveillance mechanisms that monitor ribosome assembly, including structural proofreading, molecular mimicry, RNA decay pathways, and translation-like "test-drive" reactions that assess ribosome competence. We further examine how defects in ribosome biogenesis and translation activate nucleolar surveillance, ribosome quality-control pathways, and downstream stress-response networks, including p53 signaling, the integrated stress response, and ribotoxic stress pathways. Together, these mechanisms form an interconnected quality-control system that safeguards ribosome function and cellular protein homeostasis. These studies provide important insights into the molecular basis of numerous ribosomal diseases and related disorders associated with defective ribosome biogenesis and function. Finally, we highlight emerging questions regarding ribosome heterogeneity, specialization, and the relationship between ribosome quality control and human disease.