Plays a role in alternative splicing of pre-mRNAs, possibly by contributing to the selection of non-consensus donor sites. Interacts with spliceosomal Sm proteins (By similarity). Interacts with LUC7L2 and SNRNP70, which suggests a role as a spliceosome component. Colocalizes with LUC7L2 and SNRNP70 in nuclear speckles. Strains C57BL/6J, C57BR/cdJ, C57L/J, C57BL/10J and C58/J carry the R187X allele, in which a polymorphism generates a premature stop codon, leading to either a truncated protein or an alternatively spliced isoform 3. Allele R187X is a disease susceptibility variant, which modifies the severity of the disease jolting mutant (medjo) caused by defects in Scn8a. It reduces the abundance of correctly spliced Scn8a transcripts below the threshold for survival thereby converting a chronic movement disorder into a lethal neurological disease. Due to disruption of a consensus exonic splicing enhancer in allele R187X, leading to exon 6 skipping. Only found in strains C57BL/6J, C57BR/cdJ, C57L/J, C57BL/10J and C58/J.