The basic principle of the technique is to digest a large molecule with a sequence specific hydrolase to produce moderate size fragments that can then be run on an electrophoresis gel. Provided the hydrolase only cleaves at specific sites (e.g. Between particular amino acids or bases) then the fragments should be characteristic of that molecule. The technique can be used to distinguish strains of virus or to differentiate between similar but nonidentical proteins (peptide mapping). Not to be confused with footprinting.