YJU2 is a spliceosomal protein that functions as a first-step splicing factor essential for pre-mRNA splicing. It stabilizes the catalytic step I spliceosome (C complex) structure and facilitates docking of the branch helix into the active site, enabling the first transesterification reaction that excises introns and produces 5'-exon and lariat intron-3'-intermediates 1. YJU2 interacts with the Prp16 helicase and ribonucleoprotein elements to orchestrate catalytic remodeling of the spliceosome active site 1. The protein undergoes dynamic exchange with the second-step factor Fyv6 to facilitate exon ligation, with cryo-EM structural evidence demonstrating that Fyv6 binding is mutually exclusive with YJU2, suggesting sequential factor exchange controls splicing progression 23. Additionally, YJU2 associates with the PRP19-CD5L complex and may suppress TP53-dependent apoptosis following DNA damage. Molecular dynamics simulations reveal that YJU2 binding coordinates with other spliceosomal proteins to ensure precise spliceosome activation 4. A recent Mendelian randomization study identified YJU2 as a potential causal factor associated with premature ovarian failure, though this finding requires further validation 5. YJU2 demonstrates selective function in splicing long introns through interactions with additional splicing factors including Clf1, Isy1, Prp43, and Sub2 6.