The structures and functions of the non-canonical DNAs are of great interest since they are widely distributed across the genome and are start points for various functional roles. As more genomic information is provided, their importance is getting more interest. This review aims to provide a general view about historyW?1 of non-canonical DNAs and computational strategies used to predict the individual regions that can form non-canonical DNAs across the genome.
(1) Non-canonical DNAs and their biological implication
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A majority of repeated DNA sequences in the genome can adopt at least two forms (i) orthodoxW?2 right-handed B form (Watson-Crick or canonical) or (ii) heterodox non-B form (non-canonical). This suggests that DNA fragments that are destined to adopt non-canonical conformation are polymorphs in nature. The polymorphic nature of DNA is governed by parameters such as sequence, ionic conditions, methylation, topology, carcinogen binding, protein binding, and many more (Wells et al., 1977). Analyses of repeating motifs of homo-, di-, tri-, and tetra nucleotides showsW?3 their inductive role in molecular behavior and conformations of DNA polymers and other properties (Wartell et al., 1974). FurthermoreW?4 current proceeding in the field of genomics like DNA sequencing has yielded the extensive repertoire of repeat sequences (non-B DNA-forming segments) in a variety of genomes. These findings also unravel the fact that those sequence motifs are not randomly present but localized into functionally relevant regions such as promoters or enhancers. Therefore highly regulated genes are predisposed forW?5 their presence. This non-random distribution refers to the functional implications of these motifs as transcriptional regulators.