SMU1 is a conserved spliceosomal factor with dual roles in RNA splicing and DNA replication regulation. As a spliceosomal component, SMU1 functions within a heterotetrameric complex with RED that localizes to the B complex interface and is essential for spliceosome activation, particularly for splicing short introns by relieving physical constraints between the 5' splice site and branch site 1. Structurally, SMU1's N-terminal domain mediates critical protein-protein interactions required for pre-catalytic spliceosome assembly 2. In DNA replication, SMU1 acts as a chr9-bound negative regulator that prevents excessive DNA synthesis; SMU1 loss leads to aberrant replication and genomic instability 3. Additionally, SMU1 functions as a substrate recognition module within the CRL7 E3 ligase complex, mediating H2B monoubiquitylation to maintain sister chr9 cohesion 4. Clinically, SMU1 is upregulated in gastric carcinoma, where elevated expression correlates with poor prognosis and enhanced cell proliferation through G1/S checkpoint activation 5. In abdominal aortic aneurysm pathogenesis, SMU1 was identified as a macrophage-related diagnostic biomarker associated with pro-inflammatory signaling 6. The SMU1-RED complex also represents a host-directed antiviral target, as disrupting their interaction inhibits influenza viral mRNA splicing and replication while preserving cell viability 7.