ESCRT-III-like protein involved in cytokinesis, nuclear envelope reassembly and endosomal tubulation (By similarity). Is required for efficient abscission during cytokinesis (By similarity). Involved in recruiting VPS4A and/or VPS4B to the midbody of dividing cells (By similarity). 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 (By similarity). Recruited to the reforming nuclear envelope (NE) during anaphase by LEMD2 (By similarity). Regulates early endosomal tubulation together with the ESCRT-III complex by mediating the recruitment of SPAST (By similarity). 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. Interacts with SPART (via MIT domain); leading to the recruitment of SPART to midbodies. Interacts with SPAST. Localizes to centrosome and midbody of dividing cells. Colocalized with SPART to the ends of Flemming bodies during cytokinesis. Localizes to the reforming nuclear envelope on chromatin disks during late anaphase. Belongs to the IST1 family.