Required for pre-mRNA splicing as component of the activated spliceosome. Involved in the first step of pre-mRNA splicing. Binds directly to the internal stem-loop (ISL) domain of the U6 snRNA and to the pre-mRNA intron near the 5' splice site during the activation and catalytic phases of the spliceosome cycle. Component of the pre-catalytic and catalytic spliceosome complexes. Component of the postcatalytic spliceosome P complex. Nearly exclusively nuclear. May be shuttling between the nucleus and the cytosol. The C-terminal RRM domain and the zinc finger motif are necessary for RNA-binding. Belongs to the SLT11 family.