Structures of an example of G-2 modified nucleotides. (a) Structures of the nucleotide reversibleterminators, 3′-O-N3-dATP, 3′-O-N3-dCTP, 3′-O-N3-dGTP, 3′-O-N3-dTTP. (b) Structures of cleavablefluorescent dideoxynucleotide terminators ddNTP-N3-fluorophores, with the 4 fluorophores having distinctfluorescent emissions: ddCTP-N3-Bodipy-FL-510 (λabs (max) = 502 nm; λem (max) = 510 nm), ddUTP-N3-R6G (λabs (max) = 525 nm; λem (max) = 550 nm), ddATP-N3-ROX (λabs (max) = 585 nm; λem (max) = 602 nm), and ddGTP-N3-Cy5 (λabs (max) = 649 nm; λem (max) = 670 nm).