AAR2 is a U5 snRNP assembly factor essential for spliceosome biogenesis and pre-mRNA splicing. AAR2 functions as a placeholder protein that binds the RNase H-like domain of PRPF8, a core U5 snRNP component 1. This interaction sterically excludes the Brr2p helicase and blocks U4/U6 di-snRNA binding to PRPF8, preventing premature spliceosome activation 2. AAR2 is incorporated into nascent U5 snRNP in the cytoplasm but is subsequently displaced by Brr2 after nuclear import to form mature U5 snRNP 3. The AAR2-PRPF8 interaction is phosphorylation-dependent, with CK2α1 and SGK2 kinases capable of abrogating this interaction 4. While AAR2 is essential for in vivo splicing of U3 precursors in yeast, it is dispensable for in vitro splicing, suggesting its primary role in snRNP recycling 5. Beyond its splicing function, plant AAR2 also promotes miRNA biogenesis by stabilizing the HYL1 microprocessor component 6. Notably, AAR2 was identified as a novel susceptibility gene for Hodgkin lymphoma through transcriptome-wide association analysis 7, suggesting potential disease relevance. AAR2 functions within a regulatory network involving R2TP-HSP90 chaperones during PRPF8 biogenesis 8.