RPS9 is a structural component of the eukaryotic small ribosomal subunit (40S) essential for protein synthesis 1. As part of the small subunit (SSU) processome, RPS9 participates in ribosome biogenesis within the nucleolus, coordinating with ribosomal proteins and RNA chaperones to facilitate pre-rRNA folding, modification, and processing 2. RPS9 exhibits autoregulatory control through alternative splicing mechanisms that are conserved across eukaryotes, regulating its own expression levels via nonsense-mediated decay 3. Beyond housekeeping functions, RPS9 plays pathological roles in multiple malignancies. In acute myeloid leukemia, LAPTM4B promotes disease progression by stabilizing RPS9 protein, which subsequently activates STAT3 signaling 4. In osteosarcoma, RPS9 is upregulated and promotes cell proliferation and cell cycle progression through MAPK pathway activation; RPS9 knockdown suppresses tumorigenesis 5. In non-small cell lung cancer, the lncRNA BRCAT54 suppresses tumor growth by binding RPS9 and inhibiting JAK-STAT signaling 6. Genetically, RPS9 has been identified as a susceptibility locus for Takayasu arteritis (RPS9/LILRB3), an autoimmune vasculitis 7, and as a hub gene in the shared genetic architecture between vitamin D and bone mineral density 8. RPS9 serves as a reliable internal reference gene for salivary transcriptomic analysis in clinical diagnostics 9.