Читать книгу Chemistry and Biology of Non-canonical Nucleic Acids - Naoki Sugimoto - Страница 29

As described in Chapter 1, by comparing natural RNA to DNA, there are two difference in their chemical structures. One is the ribose sugar, which bears a 2′-hydroxyl group, and the other is uracil nucleobase, which lacks the 5-methyl group of thymidine in DNA. Regarding structure formation, 2′-hydroxyl group of ribose is the most important factor that confers unique conformational features compared to the DNA. The basic feature that RNA forms an A-type duplex is based on the fact that RNA ribose adopts C3′-endo-type conformation in its sugar pucker due to the presence of 2′-hydroxyl group. The constitutive characteristic that RNA is basically single-stranded is also an important element for RNA to form various secondary and tertiary structures.

Figure 2.7 Typical structures of multi-stranded DNA helices. (a) Canonical duplex (PDB ID: 1BNA). (b) Triplex (PDB ID: 1D3X). (c) G-quadruplex (PDB ID: 139D). (d) i-motif (PDB ID: 1YBL). (e) DNA hexaplex (PDB ID: 2FZA). (f) DNA octaplex (PDB ID: 1V3P). Top views of nucleobase interactions that are located on coplanar region and important for the formation of multi-stranded helix are shown along with the structure. ^BrC indicates cytosine modified by bromine.