Fig. S4.

Single-base primer extension using four different tagged nucleotides characterized by MALDI-TOF MS. Reactions with the four tagged nucleotides (Fig. 2) along with the appropriate loop–primer template (3′-TCGAGCGCCGCGCCTTGGCGCGGCGC-5′ for T, 3′-GATCGCGCCGCGCCTTGGCGCGGCGC-5′ for G, 3′-CGATGCGCCGCGCCTTGGCGCGGCGC-5′ for A, and 3′-ATCGGCGCCGCGCCTTGGCGCGGCGC-5′ for C) yielded single-base extension products of the expected masses (8,277, 8,306, 8,280, and 8,255 for the T-, G-, A-, and C-tagged nucleotides, respectively). Peaks for the primers, the tagged nucleotides, and the released tagged pentaphosphate products are indicated as well.