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Science. 1995 Mar 24;267(5205):1817-20.

DNA topoisomerase and recombinase activities in Nae I restriction endonuclease.

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Lineberger Comprehensive Cancer Center, Department of Biochemistry and Biophysics, University of North Carolina Medical School, Chapel Hill 27599.


Nae I endonuclease must bind to two DNA sequences for cleavage. Examination of the amino acid sequence of Nae I uncovered similarity to the active site of human DNA ligase I, except for leucine 43 in Nae I instead of the lysine essential for ligase activity. Changing leucine 43 to lysine 43 (L43K) changed Nae I activity: Nae I-L43K relaxed supercoiled DNA to yield DNA topoisomers and recombined DNA to give dimeric molecules. Interruption of the reactions of Nae I and Nae I-L43K with DNA demonstrated transient protein-DNA covalent complexes. These findings imply coupled endonuclease and ligase domains and link Nae I endonuclease to the topoisomerase and recombinase protein families.

[Indexed for MEDLINE]

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