5'-CGA sequence is a strong motif for homo base-paired parallel-stranded DNA duplex as revealed by NMR analysis.
The structure of the non-self-complementary DNA heptamer d(CGACGAC) at low pH has been determined by the quantitative NMR refinement procedure designated SPEDREF (SPEctral-Driven REFinement). Acid-base titration of the molecule indicated a prominent n = 2 pKa near 6.8. In the pH range up to 6.0, the heptamer forms a remarkably stable double helix, which was conclusively shown to be an unusual homobase-paired parallel-stranded double helix (termed II-DNA). In this II-DNA helix, the 5'-CGA trinucleotide is the structural motif that accounts for the stability, with the C+-C hemiprotonated base pair (in which C+ is N3-protonated cytosine) providing for the alignment site and the unusual interstrand G-A base stack in the GpA step furnishing the additional stabilizing forces. The exchangeable proton data from two-dimensional nuclear Overhauser effect spectroscopy are in total agreement with the refined structure. We conclude that the 5'-CGA or other related sequences (e.g., 5'-CCGA) are powerful motifs in promoting the II-DNA or II-RNA conformations that may play certain biological functions.
Biophysics Division, University of Illinois, Urbana-Champaign 61801.
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D001483:Base Sequence; D002942:Circular Dichroism; D004247:DNA / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009690:Nucleic Acid Conformation; D009838:Oligodeoxyribonucleotides / Q000138:chemical synthesis / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet; D013329:Structure-Activity Relationship
D009838:Oligodeoxyribonucleotides; D004247:DNA