Fig. 3.

MALDI-TOF MS spectra of primer extension products with 3′-O-allyl-dNTPs (A–D) and 3′-O-(2-nitrobenzyl)-dNTPs (E–H). All eight 3′-O-modified nucleotides are quantitatively incorporated into the primers with high efficiency in the polymerase reaction, which indicates that the modified nucleotides are good substrates for the polymerase. The small peak near the 3′-O-(2-nitrobenzyl)-dNTP extension product corresponds to the photocleaved product generated during the laser desorption and ionization process used in MALDI-TOF MS.