Figure 1.

The principle of the procedure starting with a PCR followed by allele-specific primer extension reaction with a primer containing a photolinker and phosphorothioates at the 3′ end. The unmodified part of the primer is cut off by exposure to UV light and the modified part is then alkylated. The resulting product contains a DNA backbone with one negative charge deriving from the 5′-end. Thus, the product is negatively charge-tagged. Products are diluted and transferred onto a MALDI target for analysis.