Acts as component of a complex regulating the turnover of mRNAs in the nucleus. Binds with high affinity to RNA molecules that contain U-rich sequences in 3'-UTRs. May function in complex with UBP1 and contribute to the stabilization of mRNAs in the nucleus. However, unlike UBP1, UBA1A does not stimulate pre-mRNA splicing. Interacts with UBA1A, UBA2A, UBP1A, UBP1B and UBP1C. A number of isoforms are produced. According to EST sequences.