Double tagged Serratia Marcescens nuclease

Either wild type or mutant Serratia marcescens Nuclease (“SMN”) is engineered to display a C-terminal Chitin Binding Domain (CBD-tag), followed, at the C-terminus side of the CBD-tag, by a poly-histidine tag (His-tag), where the His-tag is preferably a 6-mer and preferably is preceded by a Gly-Ser linker, thereby generating a recombinant SMN protein that retains dual affinity tags (a CBD-tag and a His-tag) at the C-terminus, to make it easily removed from a reaction solution following digestion of nucleic acids in the reaction mixture. It can also be used for binding SMN to a solid support for use in nucleic acid digestion in a sample contacted with the solid support.