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Structural transition from dimeric to tetrameric i‐motif, caused by the presence of TAA at the 3′‐end of human telomeric C‐rich sequence
Author(s) -
Kaushik Mahima,
Prasad Manoj,
Kaushik Shikha,
Singh Anju,
Kukreti Shrikant
Publication year - 2010
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.21313
Subject(s) - antiparallel (mathematics) , chemistry , base pair , dna , sequence motif , structural motif , motif (music) , preprint , crystallography , sequence (biology) , stereochemistry , biochemistry , physics , quantum mechanics , magnetic field , acoustics
Widely dispersed in genomic DNA, the tandem C‐rich repetitive stretches may fold below physiological pH, into i‐motif structures, stabilized by C·C + pairing. Herein, structural status of a 9‐mer stretch d(CCCTAACCC), [the truncated double repeat of human telomeric sequence], and its extended version, comprising of additional TAA segment at the 3′‐end, representing the complete double repeat d(CCCTAACCCTAA), has been investigated. The pH dependent monophasic UV‐melting, Gel and CD data suggested that while the truncated version adopts a bimolecular i‐motif structure, its complete double repeat (12‐mer) sequence exists in two (bimolecular and tetramolecular) forms. A model is proposed for the tetramolecular i‐motif with conventional C · C + base pairs, additionally stabilized by asymmetric A · A base pairs at the −3′ TAA flanking ends and Watson–Crick A · T hydrogen bonding between intervening bases on antiparallel strands. Expanding the known topologies of DNA i‐motifs, such atypical geometries of i‐motifs may have implications in their recognition by proteins. © 2009 Wiley Periodicals, Inc. Biopolymers 93: 150–160, 2010. This article was originally published online as an accepted preprint. The “Published Online” date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com