Abstract: Recombinant nicking endonucleases and associated methylases have been obtained and sequenced and their specificity has been defined. A mutant form of the nicking endonuclease has been cloned where the mutation includes deletion of amino acid sequences at the C-terminal end of the protein. The nicking enzymes have been used for a number of purposes including: amplifying DNA from as few cells as can be found in a single bacterial colony in the presence of a strand displacing polymerase; and for removing genomic DNA in a biological preparation where it is deemed to be a contaminant.