Topoisomerase II is found in both prokaryotes and eukaryotes. This enzyme plays an important role in DNA replication and transcrIPPtion by relieving interlocking constraints of DNA accumulation. Topoisomerase II is activated when two double helices cross over on another. The enzyme makes a DNA gate by breaking one double helix reversibly and let a second nearby double helix pass, then reseals the break and dissociates from the DNA. Topoisomerase protein levels increase following cell proliferation and cell cycle progression from G1 to S and G2-M phase. The phosphorylation of the enzyme also changes during the cell cycle. Phosphorylation and dephosphorylation of the Topoisomerase II regulates the enzyme activity in Drosophila and Saccharomyces cerevisiae. Threonine 1342 in Human Topoisomerase II is phosphorylated throughout the cell cycle. Phosphorylation level of threonine 1342 in G2-M phase is as twice as much in G1 or S phase. Anti-phospho Topoisomerase II antibody recognizes phosphorylated threonine residue #1342 in human Topoisomerase II specifically and does not react with non-phosphorylated form.