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  • Title: The carboxyl-terminal residues of Escherichia coli DNA topoisomerase III are involved in substrate binding.
    Author: Zhang HL, DiGate RJ.
    Journal: J Biol Chem; 1994 Mar 25; 269(12):9052-9. PubMed ID: 7510701.
    Abstract:
    The nucleic acid-binding domain of Escherichia coli DNA topoisomerase III (Topo III) has been identified using a selection procedure designed to isolate inactive Topo III polypeptides. Deletion of this binding domain, contained in the carboxyl terminus of Topo III, results in a drastic reduction in the ability of the enzyme to bind to single-stranded DNA and RNA substrates. Successive truncation of the enzyme within this region results in the gradual loss of nucleic acid binding activity and in a gradual change in the mechanism of Topo III-catalyzed relaxation of negatively supercoiled DNA. The reduction of nucleic acid binding activity of the truncated polypeptides does not result in a loss of cleavage site specificity for the enzyme, suggesting that other amino acids are involved in the positioning of the nucleic acid within the nicking/closing site of the topoisomerase.
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