PRPF18 (pre-mRNA processing factor 18) is a spliceosomal protein that participates in the second step of pre-mRNA splicing 1. The protein functions as a component of the U4/U6•U5 tri-snRNP complex and is involved in generating the catalytic spliceosome for the second transesterification step of splicing [UniProt/GO annotations]. Mechanistically, PRPF18 forms stable complexes with the cyclophilin USA-CyP, which facilitates its spliceosomal function; cyclosporin A inhibition of USA-CyP specifically blocks PRPF18-dependent splicing both in vitro and in vivo 1. Beyond canonical splicing, PRPF18 exhibits broader cellular roles: it functions as a nucleoprotein chaperone that stimulates influenza virus RNA synthesis by facilitating nucleoprotein-RNA complex formation and promoting viral polymerase elongation 2. Genetically, PRPF18 variants have been identified in association with skin pigmentation in African-admixed populations at an intergenic locus with BEND7 3, and mercury exposure-associated DNA methylation changes near PRPF18 have been documented in newborn cord blood 4. Additionally, PRPF18 transcription is modulated during gamma-globin induction through NO/cGMP signaling pathways in erythroid progenitors 5, and the gene appears in customized cancer genomics panels for endometrial carcinoma classification 6. These findings indicate PRPF18 has multifaceted roles spanning RNA processing, viral pathogenesis, and disease-associated gene regulation.