Component of the spliceosome C complex required for the selective processing of microRNAs during embryonic stem cell differentiation (By similarity). Required for the biogenesis of all miRNAs from the pri-miR-17-92 primary transcript except miR-92a (By similarity). Only required for the biogenesis of miR-290 and miR-96 from the pri-miR-290-295 and pri-miR-96-183 primary transcripts, respectively (By similarity). Required during the transition of embryonic stem cells (ESCs) from the naive to primed state (By similarity). By enhancing miRNA biogenesis, promotes exit of ESCs from the naive state to an intermediate state of poised pluripotency, which precedes transition to the primed state (By similarity). Involved in pre-mRNA splicing as component of the spliceosome. {ECO:0000250|UniProtKB:Q69ZQ2, ECO:0000269|PubMed:29301961, ECO:0000305|PubMed:11991638, ECO:0000305|PubMed:25599396}. This is the function of ENSG00000240682 (ISY1, ISY1 spliceosome associated protein).