Auxiliary spliceosomal protein involved in splicing of specific pre-mRNAs that affect multiple aspects of development. Component of the spliceosome. Interacts with SMU1. Highly expressed in seedlings at 7 days after germination, young flowers before anthesis and developing siliques. Expressed at lower levels in roots, expanding leaves, open flowers, dry seeds and inflorescences. Not detected in senescing leaves. No visible phenotype, but slower growth. Belongs to the RED family.