Structural Characterization of RNA Recognition Motif-2 Domain of SART3

Squamous cell carcinoma antigen recognized by T-cells 3 (SART3) is an essential recycling factor in pre-mRNA splicing, which is required for association of U4/U6 small nuclear ribonucleoprotein (snRNP). SART3 contains two RNA recognition motifs (RRMs), and they are responsible for the tertiary interaction with U6 small nuclear RNA. Despite the importance of structural studies for understanding complicate U4/U6 snRNP recycling mechanism, only a few of them have been performed for SART3. Here, the structure of SART3 RRM2 was characterized by heteronuclear multi-dimensional nuclear magnetic resonance experiments. Nearly complete ¹H, ¹⁵N, and ¹³C chemical shifts of the backbone residues of RRM2 were assigned. In addition, the secondary structure of RRM2 were predicted by the chemical shift index and TALOS+ analyses, and the results showed that RRM2 forms a “β₁-α₁-β₂-β₃-α₂-β₄-β₅” structure, where β₄ is not common in the canonical RRM domain structures. Our results will provide structural basis for investigation of SART3-mediated U4/U6 snRNP complex formation.