ESCRT-III-like protein involved in cytokinesis, nuclear envelope reassembly and endosomal tubulation (PubMed:19129479, PubMed:26040712, PubMed:28242692). Is required for efficient abscission during cytokinesis (PubMed:19129479). Involved in recruiting VPS4A and/or VPS4B to the midbody of dividing cells (PubMed:19129480, PubMed:19129479). During late anaphase, involved in nuclear envelope reassembly and mitotic spindle disassembly together with the ESCRT-III complex: IST1 acts by mediating the recruitment of SPAST to the nuclear membrane, leading to microtubule severing (PubMed:26040712). Recruited to the reforming nuclear envelope (NE) during anaphase by LEMD2 (PubMed:28242692). Regulates early endosomal tubulation together with the ESCRT-III complex by mediating the recruitment of SPAST (PubMed:23897888). Interacts with CHMP1A, CHMP1B, VPS4A and VTA1. Interacts with SPAST, STAMBP, and USP8. May interact with VPS37B. May associate with the ESCRT-I complex. Interacts with MITD1, in competition with VSP4 (PubMed:23015756). Interacts with SPART (via MIT domain); leading to the recruitment of SPART to midbodies (PubMed:20719964). Interacts with SPAST (PubMed:23897888, PubMed:26040712). Localizes to centrosome and midbody of dividing cells (PubMed:19129480, PubMed:19129479, PubMed:20719964). Colocalized with SPART to the ends of Flemming bodies during cytokinesis (PubMed:20719964). Localizes to the reforming nuclear envelope on chromatin disks during late anaphase. Belongs to the IST1 family. Extended N-terminus.