E. Coli DNA Topoisomerase I

14K C-terminal fragment

The C-terminal fragment of topoisomerase I interacts with both single- and double-stranded DNA and enhances DNA-binding activity of the holoenzyme. This fragment also enhances the enzyme's ability to relax negative supercoils in DNA, presumably by strengthening DNA-binding.

Several topoisomerase residues implicated in binding single-stranded DNA <> correlate with known DNA-binding residues in the gene 5 protein of bacteriophage 1 <>, supporting the concept that the 14K topoisomerase I fragment functions in binding DNA.

DNA-binding activity by this C-terminal fragment may improve efficiency of strand passage activity by the 67K N-terminal fragment, thereby enhancing supercoil relaxation activity of the holoenzyme.

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