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Chemistry and Biology of Non-canonical Nucleic Acids. Naoki SugimotoЧитать онлайн книгу.

Chemistry and Biology of Non-canonical Nucleic Acids - Naoki Sugimoto


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pairs form in other structural conditions. Therefore, there are canonical structures composed by Watson–Crick base pairs in the duplex structures. On the other hand, non-canonical structures include non-Watson–Crick base pairs such as Hoogsteen base pairs.

Chemical structures of base pairs via Watson–Crick or Hoogsteen types.

      Photographs of the portrait of Linus Pauling (left), Robert Corey (middle), and Karst Hoogsteen (right).Linus Pauling (left), Robert Corey (middle), and Karst Hoogsteen (right)Photographs of the portrait of Alexander Rich (left) and Richard E. Dickerson (right).Alexander Rich (left) and Richard E. Dickerson (right)

      Behind the extensive efforts to identify the duplex structure of Watson–Crick base pairs, Hoogsteen base pairs were also found in the structure of nucleic acids in the 1960s. Felsenfeld and Rich explained how poly(rU) strands might associate with poly(rA)-poly(rU) duplexes to form triplexes [8]. From the chemical shift of NMR, they identified evidence for triplex formation via protonated G–C+ Hoogsteen base pairs at cytosine N3 in a poly(dG)-poly(dC) complex with dGMP at low pH [9]. In 1962, it was found that short guanine-rich stretches of DNA could assume unusual structures [10]. The diffraction studies of poly(guanylic acid) gels suggested that if four guanines were close enough together, they could form planar hydrogen-bonded arrangements now called guanine quartets (G-quartets). With a stack of a few G-quartets, a tetraplex structure is formed called as G-quadruplex (see Chapter 2). In the crystal structure, Hoogsteen base pairs of polynucleic acids were first found in tRNA structure [11]. In the structure Watson–Crick base pairs formed the secondary structure of tRNA, whereas Hoogsteen base pairs supported the tertiary structure. Not only Hoogsteen base pairs but also other types of non-Watson–Crick base pairs were found in tRNA structures. The tertiary structure of nucleic acids is important especially for non-coding RNAs, which do not code genetic information. The landmark of research of non-coding RNA is the discovery of ribozyme (ribonucleic acid enzyme) by Thomas Robert Cech in 1982 [12]. Ribozymes catalyze chemical reactions as well as protein enzymes. Later structural studies revealed that there are a lot of non-Watson–Crick base pairs to produce the active core of enzymatic reaction of ribozymes. Therefore, non-canonical Watson–Crick base pairs including Hoogsteen base pairs have been thought of as a tool for the tertiary structure of nucleic acids except for duplexes.

      Photograph of the portrait of Thomas Robert Cech.Thomas Robert Cech

      According to Pauling's personal communication revealed by the Nobel Foundation's disclosure, he considered Watson and Crick's Nobel award to be premature. In spite of his opinion, the Nobel Foundation decided to award the Prize to Watson and Crick. This might suggest that Watson–Crick base pairs were very common and meaningful at that time but non-Watson–Crick base pairs were artifact and meaningless. Nowadays, non-Watson–Crick base pairs are becoming common and significant as Pauling perhaps predicted. Now, the day when the essence of nucleic acids becomes beyond the concept of Watson and Crick is coming closer.

      1 1 Schrödinger, E. (1944). What Is Life? The Physical Aspect of the Living Cell and Mind. Cambridge: Cambridge University Press.

      2 2 Tamm, C., Hodes, M., and Chargaff, E. (1952). J. Biol. Chem. 195: 49–63.

      3 3 Watson, J.D. and Crick, F.H. (1953). Nature 171: 737–738.

      4 4 Pauling, L. and Corey, R.B. (1953). Nature 171: 346–346.

      5 5 (a) Hoogsteen, K. (1959). Acta Crystallogr. 12: 822–823.(b) Hoogsteen, K.R. (1963). Acta Crystallogr. 16: 907–916.

      6 6 (a) Day, R.O.,


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