Description_x000D_ Biochem/physiol Actions_x000D_ Human DNA topoisomerase I is the best studied of the DNA topoisomerase family. It catalyzes the relaxation of both positive and negative supercoils without the requirement of energy. In addition to DNA replication and transcriptional activation, DNA topoisomerase I also plays a major role in pre-mRNA splicing, cell cycle and other gene regulatory pathways during cell growth and development. The N-terminal 214 amino acids of topoisomerase I comprise a highly charged N-terminal domain (NTD) involved in protein-protein interactions with a number of cellular proteins, including SV40 T antigen, nucleolin, SR proteins, p53 and other transcription factors._x000D_ Physical form_x000D_ Clear and colorless frozen liquid solution_x000D_ Preparation Note_x000D_ Use a manual defrost freezer and avoid repeated freeze-thaw cycles. While working, please keep sample on ice.