Providing herein, among other things, are kits, compositions and methods that relate to DNA fragmentation. An embodiment of a composition provides combining: one or more enzymes capable of nick translating activity, a dNTP mix comprising at least one dNTP having a modified base, and at least one modification-sensitive nicking endonuclease that is prevented from nicking DNA if its recognition site contains the modified base. When the composition is added to a sample comprising a double-stranded DNA template that comprises recognition sites for the modification-sensitive nicking endonuclease, a reaction mix was produced which could be incubated for any time period in excess of about 5 minutes to produce fragments of a desired size of the double-stranded DNA template. In this method, the fragments produced include the modified base and, as such, are not re-nicked by the nicking endonuclease.