Component of the chromosomal passenger complex (CPC), a complex that acts as a key regulator of chromosome segregation and cytokinesis (PubMed:12707312, PubMed:10209096, PubMed:10983970). The CPC complex has essential functions at the centromere in ensuring correct chromosome condensation, alignment and segregation (PubMed:12707312, PubMed:10983970). In the complex, required to direct the Aurora B/air-2 kinase to chromosomes (PubMed:12707312, PubMed:10983970). Also functions in spindle midzone formation and in the formation of polar bodies during oogenesis (PubMed:10209096, PubMed:10983970). Required for the localization of the kinetochore component hcp-1 to chromosomes (PubMed:10983970). Involved in the positive regulation of transcription (PubMed:12682297). Involved in the transcriptional regulation of collagen genes (PubMed:17116281). Component of the CPC complex which consists of icp-1; csc-1; bir-1 and air-2. Within the complex, interacts with csc-1, icp-1 and air-2. Interacts with csc-1 in a zinc-dependent-manner; the interaction is direct. In mitosis and meiosis, localizes to chromosomes during prometaphase and metaphase, localizes to both chromosomes and the spindle midzone during anaphase and disappears from chromosomes during telophase but remains at the spindle midzone. Persists at the cytokinetic remnant during cytokinesis. Also localizes to the chromosome of polar bodies during oogenesis. Expressed in oocytes and sperm. Expressed throughout development and in adult animals, with high expression in embryos and in dividing cells (at protein level). RNAi-mediated knockdown results in high embryonic lethality (PubMed:10209096). Causes a failure in cytokinesis resulting in a lack of cellularization and in polyploidy (PubMed:10209096, PubMed:10983970). Defective extrusion of the polar body during oogenesis (PubMed:10209096, PubMed:10983970). Defects in chromosome condensation, compromised alignment and segregation of paired homologs and defects in spindle midzone formation during meiosis and mitosis (PubMed:10983970). Disruption of air-2 and hcp-1 localization to chromosomes (PubMed:10983970). Decreased phosphorylation of histone H3 'Ser-10' and decreased acetylation of histone H3 'Lys-14' and 'Lys-9' (PubMed:10983970, PubMed:12682297). Surviving animals exhibit a shorter and stouter body morphology, slow uncoordinated movements, are egg-laying defective, have abnormal germ line growth and exhibit protruding vulvas (PubMed:12682297). Decrease in the transcription of several genes including collagen genes (PubMed:12682297, PubMed:17116281). Belongs to the IAP family.