The function of USPL1 (ubiquitin specific peptidase like 1, Ensembl gene identifier ENSG00000132952) is as follows. SUMO-specific isopeptidase involved in protein desumoylation. Specifically binds SUMO proteins with a higher affinity for SUMO2 and SUMO3 which it cleaves more efficiently. Also able to process full- length SUMO proteins to their mature forms (PubMed:22878415). Plays a key role in RNA polymerase-II-mediated snRNA transcription in the Cajal bodies (PubMed:24413172). Is a component of complexes that can bind to U snRNA genes (PubMed:24413172). {ECO:0000269|PubMed:22878415, ECO:0000269|PubMed:24413172}.