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A pseudosquare knot structure of DNA in solution
N B Ulyanov1, V I Ivanov, E E Minyat
1Department of Pharmaceutical Chemistry, University of California, San Francisco 94143-0446, USA.
Biochemistry
|September 16, 1998
Summary
Researchers discovered a novel pseudosquare knot (PSQ) structure in single-stranded DNA. This DNA structure, formed by a synthetic oligonucleotide, may function as a dimerization motif in genomes.
Area of Science:
- Structural biology
- Nucleic acid chemistry
- Biophysics
Background:
- Unusual DNA structures play critical roles in biological processes.
- Short direct repeats in double-stranded DNA can adopt alternative conformations like slipped-loop structures (SLS).
- Understanding novel DNA motifs is key to deciphering genomic functions.
Purpose of the Study:
- To determine the high-resolution nuclear magnetic resonance (NMR) structure of a synthetic DNA oligonucleotide.
- To investigate a novel structural motif, the pseudosquare knot (PSQ), in single-stranded nucleic acids.
- To explore the potential biological relevance of the PSQ structure.
Main Methods:
- High-resolution NMR spectroscopy
- Deuteration of purine H8 positions for structural confirmation
- Homonuclear proton nuclear Overhauser effect (NOE) data analysis
- Complete relaxation matrix methods
Main Results:
- A homodimer of a 25-residue synthetic DNA oligonucleotide was structurally characterized.
- A novel single-stranded nucleic acid motif, the pseudosquare knot (PSQ), was identified.
- The PSQ structure consists of two adjacent helices linked by single-stranded loops.
- The relative orientation of the helices within the PSQ structure remains undetermined by NMR data.
Conclusions:
- The synthetic oligonucleotide forms a stable pseudosquare knot (PSQ) structure.
- The PSQ structure is a novel motif for single-stranded nucleic acids.
- Sequences compatible with PSQ formation are common in single-stranded genomes.
- The PSQ structure may serve as a dimerization motif in biological systems.