Topoisomerase I (TOP1) is mapped to human chromosome 20q12. TOP1 is a 91 kDa type IB enzyme and consists of N-terminal highly charged domain, a core, linker domain and a C-terminal catalytic domain with Tyr-723 active site residue.

Topoisomerase I has been used in a study to assess implications for the regulation of HIV-1 replication. Topoisomerase I has also been used in a study to investigate the tumor suppressor protein kinase Chk2 is a mediator of anoikis of intestinal epithelial cells.

Topoisomerase I human has been used for Topoisomerase I assay for screening inhibitors.

Topoisomerase I human (TOP1) interacts with DNA by wrapping and takes a bi-lobed conformation. TOPI is essential for normal development and transcriptional regulation. Variants in the TOP1 gene is observed in patients with colorectal cancer.

Topoisomerase I relaxes supercoiled DNA molecules. The enzyme initiates transient breakages and rejoins of phosphodiester bonds in superhelical turns of closed-circular DNA. Enzyme activity is independent of right- and left-handed superhelices.

Solution containing 20 mM sodium phosphate, pH 7.4, 300 mM NaCl, 50 μg/mL BSA, 50% glycerol, and between 25-100 mM imidazole (concentration will be lot dependent).

One unit will relax 0.25 μg of supercoiled plasmid DNA in 30 minutes at pH 7.9 at 37 °C.