TOP2B (DNA Topoisomerase II beta) is a 180-185kD member of the type IIA subfamily, topoisomerase family of molecules. It is ubiquitously expressed, and represents the larger of two known topoisomerases (the 2A/a-form being 170kD in size). TOP2A is essential for cell division, while TOP2B is active postmitotically. In an ATP-dependent manner, homodimeric TOP2B relives torsional stress created in DNA during transcription or as a consequence of replication. TOP2B first induces cleavage of double-stranded DNA, creating a space that allows for the physical repositioning of chromatin and a reduction in tension. This is followed by closure and ligation of the cleaved ends to recreate the original DNA structure. Human TOP2B is 1626aa in length. It contains an ATPase domain (aa101-201), an NES (aa1034-1044), more that 30 Ser/Thr phosphorylation sites and a C-terminal DTHCT region (aa1508-1611). There is one splice variant that shows a deletion of aa24-28. Over aa1187-1621, human TOP2B shares 91% aa identity with mouse TOP2B.