Structural transition from dimeric to tetrameric i-motif, caused by the presence of TAA at the 3'-end of human telomeric C-rich sequence.
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.
Nucleic Acids Research Laboratory, Department of Chemistry, University of Delhi (North Campus), Delhi-110007, India.
Mahima
M
Kaushik
Manoj
M
Prasad
Shikha
S
Kaushik
Anju
A
Singh
Shrikant
S
Kukreti
D001482:Base Composition; D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry* / Q000235:genetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D009690:Nucleic Acid Conformation; D009691:Nucleic Acid Denaturation; D020080:Tandem Repeat Sequences; D016615:Telomere / Q000235:genetics; D013816:Thermodynamics
D004247:DNA