Component of the spliceosome C complex required for the selective processing of microRNAs (miRNAs) during embryonic stem cell differentiation (PubMed:26255770, PubMed:29804889). Required for the biogenesis of all miRNAs from the pri-miR-17-92 primary transcript except miR-92a (PubMed:26255770). 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 (PubMed:29804889). Required during the transition of embryonic stem cells (ESCs) from the naive to primed state (PubMed:29804889). By enhancing miRNA biogenesis, promotes exit of ESCs from the naive state to an intermediate state of poised pluripotency, which precedes the transition to the primed state (PubMed:29804889). Involved in pre-mRNA splicing as component of the spliceosome. Identified in the spliceosome C complex. Component of the XAB2 complex, a multimeric protein complex composed of XAB2, PRPF19, AQR, ZNF830, ISY1, and PPIE. Identified in a pentameric intron-binding (IB) complex composed of AQR, XAB2, ISY1, ZNF830 and PPIE that is incorporated into the spliceosome as a preassembled complex. The IB complex does not contain PRPF19. Interacts with CPSF3; this interaction is in an RNA independent manner (PubMed:26255770). Interacts with the microprocessor complex subunits DGCR8 and DROSHA; this interaction is in an RNA dependent manner (PubMed:26255770). During embryoid body (EB) formation, expression peaks at day 1 of EB differentiation (at protein level) (PubMed:29804889). Expressed during embryonic stem cell differentiation in vitro, with high expression during the earliest time point of differentiation during a 'poised' pluripotency phase that occurs in between embryonic day 4.5 and embryonic day 5.5 (PubMed:26255770, PubMed:29804889). Belongs to the ISY1 family.