Compositions and methods for nucleotide sequencing

A method for sequencing a nucleic acid molecule, comprising:

• (a) contacting a nucleic acid template, a nucleic acid primer complementary to a portion of said template, an extension enzyme, and a reversibly blocked nucleotide under conditions wherein said primer is extended to incorporate said nucleotide into a sequence complementary to said nucleic acid template,
• said reversibly blocked nucleotide comprising a sugar moiety and a base moiety, wherein said base moiety is linked to a label by linker, and
• wherein, attached at the 2′ or 4′ position of said sugar moiety, is a reversible blocking group comprising —CH2—CH═CH2, CH2—N3, —CH2—S—S-tBu, —CH2—S—Me, —CH2—O—CH2—CH2—CN, —CH2—CH2—CN, —C(O)—CH3, —CH3, 2-nitrobenzyl, tetrahydropyran, 4-nitrobenzoyl, 2-aminobenzoyl, —C(O)linker-dye, 2-nitrobenzyl-linker-dye, —C(O)—O—CH2CH═CH-linker-dye, —NH—C(O)—CH3, —F, —NH2, phosphate, or sulfate,
• (b) identifying the nucleotide in said sequence complementary to said nucleic acid template;
• (c1) removing or modifying the label;
• and
• (c2) removing the blocking group,
• wherein identifying said nucleotide identifies at least a portion of the sequence of said nucleic acid molecule.