Control of topological states of DNA by transient breakage and subsequent rejoining of DNA strands (PubMed:6308011, PubMed:2547764, PubMed:1328202, PubMed:8383533, PubMed:10786800, PubMed:8978614). Topoisomerase II makes double-strand breaks (PubMed:6308011, PubMed:2547764, PubMed:1328202, PubMed:8383533, PubMed:10786800, PubMed:9545289). Essential during mitosis and meiosis for proper segregation of daughter chromosomes (PubMed:10751154, PubMed:14600258, PubMed:18752348, PubMed:25340780). During meiosis, it disrupts heterochromatic connections between achiasmate and chiasmate homologs after spindle assembly so that chromosomes can separate at prometaphase I (PubMed:25340780). During mitosis, it functions in the separation of sister chromatids by establishing amphitelic kinetochore attachments in mitotic spindles (PubMed:18752348). May have a role in chromatin condensation and chromosome structure (PubMed:14600258, PubMed:18752348, PubMed:25340780). May be involved in X-chromosome dosage compensation, perhaps by modifying the topological state of compensated genes (PubMed:23989663). Regulates activity of the gypsy chromatin insulator complex by binding to mod(mdg4) and preventing its degradation (PubMed:21304601). ATP-dependent breakage, passage and rejoining of double-stranded DNA. Binds two Mg(2+) per subunit. The magnesium ions form salt bridges with both the protein and the DNA. Can also accept other divalent metal cations, such as Mn(2+) or Ca(2+). Homodimer (By similarity). Interacts with mod(mdg4) (PubMed:21304601). Interacts with barr (PubMed:8978614, PubMed:11172718). Interacts with ph-p (PubMed:11172718). Interacts with mle; the interaction mediates association with the MSL dosage compensation complex (PubMed:23989663). Nuclear at interphase, becoming diffusely dispersed in the cytoplasm at later cell cycle stages (PubMed:10885744, PubMed:10751154). However in early developing embryos, some may remain associated with condensed chromosomes at metaphase (PubMed:10885744). Detected in germline and follicle cells (at protein level). Predominantly expressed in follicle cells where expression persists throughout oogenesis (at protein level). In germline cells, expression levels decrease as cells develop and move to the posterior region of the germarium. Phosphorylated (PubMed:1328202, PubMed:8383533, PubMed:10751154). Phosphorylation by casein kinase II enhances ATPase activity (PubMed:1328202). Homozygous lethal (PubMed:21304601). Embryogenesis appears normal, probably due to maternal contribution of the protein (PubMed:21304601). However after hatching flies show a 2-3 day delay in development and most die before the third instar stage (PubMed:21304601). Conditional RNAi-mediated knockdown in the female germline does not affect fertilization but embryos fail to initiate proper mitotic divisions and do not hatch (PubMed:25340780). Embryos contain only two nuclei; a small nucleus with a centriolar spindle and a large round nucleus (PubMed:25340780). Knockdown in stage 3 oocytes often results in the heterochromatic regions of all four chromosomes failing to separate during prometaphase I and metaphase I of meiosis I (PubMed:25340780). In some instances, the anchored heterochromatic regions become stretched as the centromeres attempt to move towards the spindles poles creating long, abnormal heterochromatin structures that project from the main chromosome mass with centromeres at their tips (PubMed:25340780). Spindle assembly is not affected (PubMed:25340780). Spindles are bipolar although one or both sides of the spindle are elongated due to the abnormal heterochromatin projections (PubMed:25340780). Eukaryotic topoisomerase I and II can relax both negative and positive supercoils, whereas prokaryotic enzymes relax only negative supercoils. Belongs to the type II topoisomerase family.