Table 2.

Summary of modified nucleic acids found in UTexas Aptamer Database aptamers

Nucleic acid modifications
Modification (# of aptamers with modification)	Description
2′-fluoro-RNA (80)	Both pyrimidine nucleotides contain 2′-fluoro modifications (i.e. 2′-F-modified CTP and UTP & 2′-OH ATP and GTP)
2′-amino-RNA (22)	Includes 2 different types of modifications on one or both pyrimidine nucleotides: • Single CTP 2′-amino-modification (2′-NH2-CTP, 2′-OH-purine ATP/GTP/UTP) • Both pyrimidines (CTP and UTP) amino-modified (2′-NH2-pyrimidine, 2′-OH-purine RNA)
2′-fluoro and 2′-amino-RNA (1)	Both pyrimidine nucleotides have 2 different modifications (i.e. 2′-F-CTP, 2′-NH2, -UTP and 2′-OH ATP and GTP)
2′-O-Me-RNA (5)	Both pyrimidine nucleotides have 2′-O-Me modifications (i.e. 2′-O-methyl CTP and UTP and 2′-OH ATP and GTP)
4′-thio-RNA (2)	Both pyrimidine nucleotides have 4′-thio modifications instead of the 4′-O in the ribose ring (i.e. 4′-thio CTP and UTP, canonical ATP and GTP)
5-uracil-modified-DNA (6)	Modifications include 5-pentynyl-dU (5-(1-pentynyl)-2′-deoxyuridine) and Nap-dU (5-[N-(1-naphthylmethyl) Carboxamide]-2′-deoxyuridine)
5-uracil-modified-RNA (1)	Modification includes NH2-UTP (5-(3-aminopropyl) UTP)
2′,4′-BNA/LNA-DNA (5)	2′-O,4′-C-methylene bridged/locked nucleic acid
FANA XNA (3)	2′-deoxy-2′-fluoroarabinonucleotide (FANA) has unnatural structures (termed xeno-nucleic acids or XNA), containing 2′-fluorine in β-conformation and ring in the C2’/O4’-endo conformation (not typical 2′-fluoro α-conformation, ring in C3’-endo conformation)