A tricyclic nucleoside having Formula I: wherein: Bx is a pyrimidine, substituted pyrimidine, purine or substituted purine; Q is CH 2 -CH 2, CH=CH, O, S, or NR 1; R 1 is H, C 1 -C 6 alkyl, substituted C 1 -C 6 alkyl, C 2 -C 6 alkenyl, substituted C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, substituted C 2 -C 6 alkynyl or a protecting group; one of q 1 and q 2 is hydroxyl or a protected hydroxyl and the other of q 1 and q 2 is H; one of q 3 and q 4 is hydroxyl, a protected hydroxyl or a reactive phosphorus group and the other of q 3 and q 4 is H; wherein said reactive phosphorous group is a phosphoramidite, H-phosphonate or phosphate triester; wherein each substituted group is, independently, mono or poly substituted with substituent groups independently selected from halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, OJ 1, SJ 1, NJ 1 J 2, N 3, CN, C(=O)OJ 1, C(=O)NJ 1 J 2, C(=O)J 1, O-C(=O)NJ 1 J 2, N C(=O)NJ 1 J 2, N C(=S)NJ 1 J 2 and a protecting group; each J 1 and J 2 is, independently, H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 aminoalkyl or a protecting group; n is 1; and m is 0 when Q is CH 2 -CH 2 or CH=CH and m is 1 when Q is O, S, or NR 1; wherein the protecting group is selected from i) the following hydroxyl protecting groups: acetyl, t-butyl, t-butoxymethyl, methoxymethyl, tetrahydropyranyl, 1-ethoxyethyl, 1-(2-chloroethoxy)ethyl, p-chlorophenyl, 2,4-dinitrophenyl, benzyl, 2,6-dichlorobenzyl, diphenylmethyl, p-nitrobenzyl, bis(2-acetoxyethoxy)methyl, 2-trimethylsilylethyl, trimethylsilyl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl, triphenylsilyl, [(triisopropylsilyl)oxy]methyl, benzoylformate, chloroacetyl, trichloroacetyl, trifluoroacetyl, pivaloyl, benzoyl, p-phenylbenzoyl, 9-fluorenylmethyl carbonate, mesylate, tosylate, triphenylmethyl; (trityl), monomethoxytrityl, dimethoxytrityl, trimethoxytrityl, 1(2-fluorophenyl)-4-methoxypiperidin-4-yl (FPMP), 9-phenylxanthine-9-yl (Pixyl), 9-(p-methoxyphenyl)xanthine-9-yl; or ii) the following amino protecting groups: carbamate protecting groups such as 2-trimethylsilylethoxycarbonyl (Teoc), 1-methyl-1-(4-biphenylyl)ethoxycarbonyl (Bpoc), t-butoxycarbonyl, allyloxycarbonyl (Alloc), 9-fluorenylmethyloxycarbonyl (Fmoc), benzyloxycarbonyl (Cbz); amide-protecting groups, such as formyl, acetyl, trihaloacetyl, benzoyl and nitrophenylacetyl; sulfonamide-protecting groups, such as 2-nitrobenzenesulfonyl; and imine- and cyclic imide-protecting groups, such as phthalimido and dithiasuccinoyl; or iii) the following thiol protecting groups:triphenylmethyl (trityl), benzyl (Bn); wherein each protected hydroxyl group comprises a protecting group independently selected from acetyl, benzyl, t-butyldimethylsilyl, t-butyldiphenylsilyl or 4,4'-dimethoxytrityl. Bx is a pyrimidine, substituted pyrimidine, purine or substituted purine; Q is CH 2 -CH 2, CH=CH, O, S, or NR 1; R 1 is H, C 1 -C 6 alkyl, substituted C 1 -C 6 alkyl, C 2 -C 6 alkenyl, substituted C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, substituted C 2 -C 6 alkynyl or a protecting group; one of q 1 and q 2 is hydroxyl or a protected hydroxyl and the other of q 1 and q 2 is H; one of q 3 and q 4 is hydroxyl, a protected hydroxyl or a reactive phosphorus group and the other of q 3 and q 4 is H; wherein said reactive phosphorous group is a phosphoramidite, H-phosphonate or phosphate triester; wherein each substituted group is, independently, mono or poly substituted with substituent groups independently selected from halogen, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, OJ 1, SJ 1, NJ 1 J 2, N 3, CN, C(=O)OJ 1, C(=O)NJ 1 J 2, C(=O)J 1, O-C(=O)NJ 1 J 2, N C(=O)NJ 1 J 2, N C(=S)NJ 1 J 2 and a protecting group; each J 1 and J 2 is, independently, H, C 1 -C 6 alkyl, C 2 -C 6 alkenyl, C 2 -C 6 alkynyl, C 1 -C 6 aminoalkyl or a protecting group; n is 1; and m is 0 when Q is CH 2 -CH 2 or CH=CH and m is 1 when Q is O, S, or NR 1; i) the following hydroxyl protecting groups: acetyl, t-butyl, t-butoxymethyl, methoxymethyl, tetrahydropyranyl, 1-ethoxyethyl, 1-(2-chloroethoxy)ethyl, p-chlorophenyl, 2,4-dinitrophenyl, benzyl, 2,6-dichlorobenzyl, diphenylmethyl, p-nitrobenzyl, bis(2-acetoxyethoxy)methyl, 2-trimethylsilylethyl, trimethylsilyl, triethylsilyl, t-butyldimethylsilyl, t-butyldiphenylsilyl, triphenylsilyl, [(triisopropylsilyl)oxy]methyl, benzoylformate, chloroacetyl, trichloroacetyl, trifluoroacetyl, pivaloyl, benzoyl, p-phenylbenzoyl, 9-fluorenylmethyl carbonate, mesylate, tosylate, triphenylmethyl; (trityl), monomethoxytrityl, dimethoxytrityl, trimethoxytrityl, 1(2-fluorophenyl)-4-methoxypiperidin-4-yl (FPMP), 9-phenylxanthine-9-yl (Pixyl), 9-(p-methoxyphenyl)xanthine-9-yl; or ii) the following amino protecting groups: carbamate protecting groups such as 2-trimethylsilylethoxycarbonyl (Teoc), 1-methyl-1-(4-biphenylyl)ethoxycarbonyl (Bpoc), t-butoxycarbonyl, allyloxycarbonyl (Alloc), 9-fluorenylmethyloxycarbonyl (Fmoc), benzyloxycarbonyl (Cbz); amide-protecting groups, such as formyl, acetyl, trihaloacetyl, benzoyl and nitrophenylacetyl; sulfonamide-protecting groups, such as 2-nitrobenzenesulfonyl; and imine- and cyclic imide-protecting groups, such as phthalimido and dithiasuccinoyl; or iii) the following thiol protecting groups:triphenylmethyl (trityl), benzyl (Bn);