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. Identified in the spliceosome C complex (PubMed:11991638, PubMed:29301961). Component of the XAB2 complex, a multimeric protein complex composed of XAB2, PRPF19, AQR, ZNF830, ISY1, and PPIE (PubMed:17981804). 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 (PubMed:25599396). The IB complex does not contain PRPF19 (PubMed:25599396). Interacts with CPSF3; this interaction is in an RNA independent manner (By similarity). Interacts with the microprocessor complex subunits DGCR8 and DROSHA; this interaction is in an RNA dependent manner (By similarity). Based on a readthrough transcript which may produce a ISY1-RAB43 fusion protein. Belongs to the ISY1 family. Extended N-terminus.