Human DNA topoisomerase I is the best studied of the DNA topoisomerase family. It catalyzes the relaxation of both positive and negative supercoiled DNAs 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. Tyrosine 723 was identified as an active site for the DNA binding activity of DNA topoisomerase I. The covalent intermediate of topo I and DNA complex includes nucleophilic attack by the O4-oxygen of tyrosine 723 on a phosphester linkage in the DNA. Mutation from tyrosine to phenylalanine at position 723 preferentially binds the supercoiled DNA rather than relaxed DNA in the mixture of supercoiled and relaxed DNAs. But mutation at tyr723 neither affects its kinase activity that phosphorylates splicing factors of SR protein family nor its transcription activity of class II genes in vitro.
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Clear and colorless frozen liquid solution
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Use a manual defrost freezer and avoid repeated freeze-thaw cycles. While working, please keep sample on ice.
The Journal of biological chemistry, 256(10), 4805-4809 (1981-05-25)
Conditions which result in DNA strand breakage by the rat liver DNA nicking-closing enzyme lead to the covalent attachment of the 3'-end of the broken strand to the enzyme. Treatment of this complex with pancreatic DNase leaves a residue of
DNA topoisomerase poisons as antitumor drugs.
L F Liu
Annual review of biochemistry, 58, 351-375 (1989-01-01)
Annual review of biochemistry, 70, 369-413 (2001-06-08)
DNA topoisomerases solve the topological problems associated with DNA replication, transcription, recombination, and chromatin remodeling by introducing temporary single- or double-strand breaks in the DNA. In addition, these enzymes fine-tune the steady-state level of DNA supercoiling both to facilitate protein
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