Nucleic acid bases tetrads

Besides guanine and isoguanine, other nucleic acids bases are also found to be able to form the tetrad structures through H-bonds between the neighboring bases [24-27]. 

Quantum-chemical ab initio studies have been performed on triads" " on tetrads " and on a pentad structure. Except for one recent paper we are not aware of further semiempirical calculations on base polyads. Even though semiempirical approaches 5deld occasionally sensible results we know fi om studies on nucleic acid base pairs that a consistent theoretical picture of their structure and energetics did only emerge when ab initio calculations with a consistent treatmait of electron correlation have become feasible. Hence, it is hi y recommraided to adopt non-empirical approaches for studies on base polyads. A detailed comparison of non-empirical, semiempirical and empirical approaches for the description of DNA base interactions has been performed by Hobza et al. ... 

Nucleic acids can form complex structures that consist of more than two strands. Recently, the interest in structures and functions of the DNA bases polyads has significantly increased. It has been shown that guanine tetrads are vital components of many biologically important processes. 

Much like the search for protein-binding compounds requires consideration of tertiary structure in addition to peptide sequence, thinking about selective nucleic acid binding solely in the context of primary sequence is often an oversimplification. In the context of DNA recognition, a particularly important example of this is the case of G-quadruplexes. As their name implies, these structures consist of stacked tetrads of guanosine bases, typically ordered around a monovalent cation. One representative structure, a quadruplex derived from human telomeric DNA, is shown in Fig. 5 many variants of this motif formed by either parallel or antiparallel DNA strands have been observed. 

This review is focused on hi er-order base motifs where more than two bases are linked by H-bonds. We call these nucleic acid building blocks base triads, tetrads, pentads,. .. and in general base polyads. Alternative names for these base motifs are triple, quartet, quintet,. Multistranded structure that... 

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