SMU1 is a component of the spliceosome involved in pre-mRNA splicing []. In Arabidopsis SMU1 and SMU2 are required for low-Mg tolerance through regulating the pre-mRNA splicing of the Mg2+ transporter gene MRS2-7 []. In Caenorhabditis elegans SMU1 and SMU2 function together to regulate splice site choice in the pre-mRNAs of unc-52 and other genes [].