Component of the DNA topoisomerase VI complex. Binds to DNA. Required for chromatin organization and progression of endoreduplication cycles. The loss of BIN4 activates the ATM- and ATR-dependent DNA damage responses in postmitotic cells and induces the ectopic expression of the mitotic G2/M-specific cyclin B1;1 gene in non-dividing cells. Interacts with TOP6A, RHL1 and itself, but not with TOP6B. A number of isoforms are produced. According to EST sequences. Expressed in expanding cotyledons, vascular cells, elongating root cells, developing leaf trichomes, root and apical meristems and lateral root primordia. Ubiquitously expressed at low levels during the mitotic cell cycle. Plants show a severe dwarf phenotype. In bin4 mutants, a specific DNA damage repair checkpoint is activated preventing further progression of endoreplication cycles.