Cleaves the 2'-5' phosphodiester linkage at the branch point of lariat intron pre-mRNAs after splicing and converts them into linear molecules that are subsequently degraded. It thereby facilitates ribonucleotide turnover. It may also participate in retrovirus replication via an RNA lariat intermediate in cDNA synthesis. Plays en essential role during embryogenesis. Widely expressed. Expressed in roots, stems, cauline and rosette leaves, flower buds and siliques. Belongs to the lariat debranching enzyme family.