PLRG1 (pleiotropic regulator 1) is a highly conserved spliceosomal protein functioning as a critical component of the PRP19-CDC5L complex, also known as the nineteen complex (NTC) 1. Its primary role involves pre-mRNA splicing through integration into the spliceosome catalytic machinery 23. Mechanistically, PLRG1 contains a WD40 domain that undergoes dynamic conformational changes upon binding spliceosomal partners, facilitating spliceosome assembly 4. The protein interacts directly with hnRNP-M and CDC5L to regulate alternative splice site selection 5. Beyond splicing, PLRG1 participates in DNA repair as part of the NTC, which functions as a multimeric E3 ubiquitin ligase activated through stepwise assembly with Prp19, SPF27, and CDC5L 6. PLRG1 is significantly upregulated in multiple tumor types, where elevated expression promotes cancer cell proliferation and genome stability maintenance while being dispensable in normal cells 1. In hepatocellular carcinoma, PLRG1 cooperates with DHX37 to drive cyclin D1 transcription via superenhancer elements 7 and promotes epithelial-mesenchymal transition when transcriptionally activated by YBX1 8. Its nuclear speckle localization is dynamically regulated by the deubiquitylase USP42, which directs PLRG1 integration into phase-separated condensates 9. These findings establish PLRG1 as a potential anticancer therapeutic target.