Component of the chromosomal passenger complex (CPC), a complex that acts as a key regulator of mitosis. The CPC complex has essential functions at the centromere in ensuring correct chromosome alignment and segregation and is required for chromatin-induced microtubule stabilization and spindle assembly. Acts as a scaffold regulating CPC localization and activity. The C-terminus associates with aurkb/aurora-B, the N-terminus associated with cdca8/borealin and/or cdca9/dasra-A tethers the CPC to the inner centromere, and the microtubule binding activity within the central SAH domain directs aurkb/aurora-B toward substrates near microtubules. Activates aurkb. Component of the CPC composed of survivin/birc5, incenp, cdca8/borealin and/or cdca9/dasra-A, and aurkb/aurora-B. Interacts (via C-terminus) with aurkb (via N-terminus and kinase domain). Interacts (via N-terminus) with birc5.1, birc5.2, cdca8 and cdca9. Interacts with mtus1. Localizes on chromosome arms and inner centromeres from prophase through metaphase and then transferring to the spindle midzone and midbody from anaphase through cytokinesis (PubMed:10996078). Colocalizes to the equatorial cell cortex at anaphase (PubMed:10996078). Colocalizes with AURKB at mitotic chromosomes (PubMed:10996078). The IN box mediates interaction with aurkb/aurora-B. The SAH (single alpha-helix) region is characterized by a high content of charged residues which are predicted to stabilize the alpha-helical structure by ionic bonds. It can refold after extension suggesting an in vivo force-dependent function. The isolated SAH domain is monomeric. Belongs to the INCENP family. Originally predicted to contain a coiled coil domain but shown to contain a stable SAH domain instead.