YB-1 is a nuclear protein that binds to splice sites in pre-mRNA and regulates splice site selection. Binds and stabilizes cytoplasmic mRNA. Contributes to the regulation of translation by modulating the interaction between the mRNA and eukaryotic initiation factors CCAAT-containing Y-box of HLA class II genes. Component of cytoplasmic messenger ribonucleoprotein particles (mRNPs). Interacts with AKT1, SFRS9, THOC4, MSH2, XRCC5, WRN and NCL. Can bind to DNA as a homomeric form, (EFI-A)n or as a heteromeric form in association with EFI-B. Homodimer in the presence of ATP.