SAP stands for Shrimp Alkaline Phosphatase whereas EXO stands for Exonuclease I. SAP and EXO are two hydrolytic enzymes. The purpose of this procedure is used to chew up excess primers and remove excess dNTPs from your PCR product. This procedure is necessary to ensure clean and readable DNA sequences. The SAP/EXO protocol is the simplest way to clean up PCR products before sequencing. Exonuclease I removes residual single-sranded primers and any extraneous single-stranded DNA produced in the PCR. Shrimp alkaline phosphatase removes the remaining dNTPs from the PCR mixture.