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At least 631 records · Page 35Linked to original sources
PubMed2006

Human RFP2 gene promoter: unique structure and unusual strength.

Human gene RFP2 is a candidate tumor suppressor located at 13q14.3 and deleted in multiple tumor types. To explore regulation of RFP2, we determined structure of the 5'-untranslated region of RFP2 gene and its promoter. RFP2 promoter area is TATA-less, highly enriched in G and C nucleotides, and contains multiple quadruplex forming GGGGA-repeats. Deletion analysis of 5'-flanking sequences demonstrated that repeat containing fragment possesses activity seven times exceeding that of the combined SV40 promoter/enhancer. Other unusual features of the RFP2 promoter include anomalously high electrostatic fields induced by sequence-dependent dipoles and very low nucleosome forming potential. A "minimized" version of the RFP2 promoter could be used for overexpression of the various transgenes in the mammalian cells.

Base Sequence↗
PubMed2005

Synthesis and testing of a triaza-cyclopenta[b]phenanthrene scaffold as a DNA binding agent.

A novel DNA binding agent based upon a triaza-cyclopenta[b]phenanthrene scaffold, compound 1, has been synthesized. dsDNA binding analysis of this compound using the ethidium bromide displacement assay indicated a preference for GC-rich sequences. However, equilibrium dialysis experiments against a variety of nucleic acids showed that the target compound bound about 20-fold tighter to G-quartet DNA than to dsDNA under physiological salt concentrations. The binding of 1 to G-quartet DNA was verified by the ability of the compound to promote the formation of the quartet and to compete with TmPyP4 for binding to the quadruplex. Given the importance of G-quartet binding agents in the treatment of cancer and in the understanding of drug-DNA interactions, 1 and its related analogs should find utility as a new class of G-quartet specific agents.

Binding, Competitive↗
PubMed1998

Following G-quartet formation by UV-spectroscopy.

Oligodeoxynucleotides which include stretches of guanines form a well-known tetrameric structure. We show that the recording of reversible absorbance changes at 295 nm allows to precisely monitor intramolecular guanine (G)-quartet formation and dissociation. Accurate Tm and thermodynamic values could be easily extracted from the data, whereas classical recordings at 260 nm led to a much larger uncertainty and in extreme cases, to completely inaccurate measurements. This inverted denaturation profile was observed for all G-quartet-forming oligonucleotides studied so far. This technique is very useful in all cases where intramolecular or intermolecular quadruplex formation is suspected.

DNA↗
PubMed2003

Facile preparation of DNA-tagged carbohydrates.

We report here that unprotected carbohydrates (maltose, lactose, cellobiose, and maltoheptaose) can be attached to the aminoalkylated oligonucleotides under mild reductive-amination conditions (aqueous borate buffer, pH 8.0, NaBH(3)CN, 60 degrees C) without notable side reactions. Quadruplex-forming G-rich oligonucleotide, 5'-aminoalkyl d(TGGGGT), is glycosylated with maltoheptaose to afford a novel DNA-assisted tetrasaccharide cluster motif.

Alkylation↗
PubMed2002

Hemin-stimulated docking of cytochrome c to a hemin-DNA aptamer complex.

DNA aptamers were selected for their ability to bind simultaneously to the protein cytochrome c and to the metalloporphyrin hemin. Such aptamers each contained a conserved guanine-rich core, analogous to sequences shown previously to form a hemin-binding site when folded. The detailed study of CH6A, a deletion mutant of one clone, indicated that in the presence of hemin the guanine-rich core of the aptamer folded to form a guanine quadruplex. Both hemin and potassium ions were required for this folding. The binding of fully oxidized cytochrome c to this DNA-hemin complex resulted in an absorbance difference spectrum in the Soret region, which could be used as an indicator of binding behavior. It was found that cytochrome c bound more tightly to the folded CH6A DNA-hemin complex than to the folded CH6A DNA alone. A single hemin molecule and a single cytochrome c bound to each molecule of folded CH6A. Footprinting experiments showed the binding site of the cytochrome c to be a partial duplex element of the aptamer, immediately flanking its guanine-rich hemin-binding site. The order of addition of hemin and cytochrome c appeared not to affect either the formation rate or the structure of the final ternary complex. The ternary complex represents the docking of a nucleic acid-heme complex to cytochrome c (a protein-heme complex). Future experiments will focus on investigating the optimal electron-transfer path between the two iron centers through intervening protein and DNA.

Amino Acid Sequence↗
PubMed1999

Structural analysis of G-DNA in solution: A combination of polarized and depolarized dynamic light scattering with hydrodynamic model calculations.

Specific intra- and intermolecular quadruplex conformations of model G-DNA oligonucleotides have been identified from their translational and rotational diffusion coefficients in aqueous solution. The transport properties were determined by polarized and depolarized dynamic light scattering. A comparison with hydrodynamic model calculations provides detailed information about the size and shape of the molecules and allows one to distinguish between alternative intra- and intermolecular association. The potential of this combination of methods to elucidate biomolecular structures in solution, to characterize conformational changes, and follow intermolecular interaction processes due to a response to external stimuli has been discussed.

DNA↗
PubMed2003

Four-stranded DNA structure stabilized by a novel G:C:A:T tetrad.

The solution structure of a cyclic oligonucleotide d has been determined by two-dimensional NMR spectroscopy and restrained molecular dynamics. Under the appropriate experimental conditions, this molecule self-associates, forming a symmetric dimer stabilized by four intermolecular Watson-Crick base pairs. The resulting four-stranded structure consists of two G:C:A:T tetrads, formed by facing the minor groove side of the Watson-Crick base-pairs. Most probably, the association of the base-pairs is stabilized by coordinating a Na(+) cation. This is the first time that this novel G:C:A:T tetrad has been found in an oligonucleotide structure. This observation increases considerably the number of sequences that may adopt a four-stranded architecture. Overall, the three-dimensional structure is similar to those observed previously in other quadruplexes formed by minor groove alignment of Watson-Crick base pairs. This resemblance strongly suggests that we may be observing a general motif for DNA-DNA recognition.

Base Pairing↗
PubMed2005

G-quartet-induced nanoparticle assembly.

The design and synthesis of a new class of gold nanoparticle with guanosine monophosphate derivatives or G-rich oligonucleotides as their surface ligands are described. These nanoparticles spontaneously form macroscopic assemblies at low temperature and relatively high salt concentrations, which is attributed to the cooperative formation of guanosine quartets and G-quadruplexes between the individual nanoparticles. Significantly, the solution behavior of these nanoparticles is highly controllable by adjusting solution parameters (including temperature, ionic strength, and ion species) and the sequence of the G-rich oligonucleotide

DNA↗
PubMed2025

Hyperpolarized NMR Reveals Low-Populated Folding Intermediates in DNA.

Nuclear magnetic resonance (NMR) spectroscopy is the only biophysical technique capable of characterizing nucleic acid structures at atomic resolution under near-physiological liquid-state conditions. Still, it is fundamentally limited by intrinsically low sensitivity, particularly when analyzing high-molecular-weight, low-abundance, or polymorphic targets, such as DNAs (DNA). In this study, we demonstrate that hyperpolarized aqueous buffers generated via dissolution dynamic nuclear polarization (dDNP) significantly enhance the 1H NMR signals of multiple DNA motifs. The resonances of labile imino and amino protons of DNAs dissolved in hyperpolarized buffers are enhanced up to ∼200-fold and ∼370-fold, respectively. These intense signals serve a 2-fold purpose: (i) as structural fingerprints of DNA folding topologies and (ii) they enable the direct observation of low-populated folding intermediates in DNA polymorphs, such as G-quadruplexes (G4) and i-motifs (iM), which remain undetectable by standard methods. Thus, our findings establish hyperpolarized NMR as a high-sensitivity method for probing DNA structures and folding intermediates across a wide range of motifs, opening possible avenues in liquid biopsy applications and cell-free DNA.

DNA↗
PubMed2002

Solid-phase synthesis of symmetrical 3,6-bispeptide-acridone conjugates.

[reaction: see text] A novel high-yielding method for the solid-phase synthesis of 3,6-bispeptide-acridone conjugates is reported. It involves initial coupling of bifunctionalized acridone to a resin-bound peptide followed by an on-bead site-site reaction to couple the second peptide. This method leads to clean symmetrical bispeptide derivatives and appears to be general. This strategy will enable the generation of a library of 3,6-bispeptide-acridones to be screened for selective binding to telomeric G-quadruplex DNA.

Acridines↗
PubMed2001

1H-1H correlations across N-H...N hydrogen bonds in nucleic acids.

In 2HJ(NN)-COSY experiments, which correlate protons with donor/acceptor nitrogens across Nd...HNa bonds, the receptor nitrogen needs to be assigned in order to unambiguously identify the hydrogen bond. For many situations this is a non-trivial task which is further complicated by poor dispersion of (Na,Nd) resonances. To address these problems, we present pulse sequences to obtain direct, internucleotide correlations between protons in uniformly 13C/15N labeled nucleic acids containing Nd...HNa hydrogen bonds. Specifically, the pulse sequence H2(N1N3)H3 correlates H2(A,omega1):H3(U,omega2) protons across Watson-CrickA-U and mismatched G.A base pairs, the sequences H5(N3N1)H1/H6(N3N1)H1 correlate H5(C,omega1)/H6(C,omega1):H1(G,omega2) protons across Watson-Crick G-C base pairs, and the H2(N2N7)H8 sequence correlates NH2(G,A,C;omega1):H8(G,A;omega2) protons across G.G, A.A, sheared G.A and other mismatch pairs. These 1H-1H connectivities circumvent the need for independent assignment of the donor/acceptor nitrogen and related degeneracy issues associated with poorly dispersed nitrogen resonances. The methodology is demonstrated on uniformly 13C/15N labeled samples of (a) an RNA regulatory element involving the HIV-1 TAR RNA fragment, (b) a multi-stranded DNA architecture involving a G.(C-A) triad-containing G-quadruplex and (c) a peptide-RNA complex involving an evolved peptide bound to the HIV-1 Rev response element (RRE) RNA fragment.

Base Pair Mismatch↗
PubMed2002

Differentiation between unlabeled and very-low-level fully 15N,13C-labeled nucleotides for resonance assignments in nucleic acids.

Based on different characteristics between unlabeled and fully 15N,13C-labeled nucleotides, we develop a method for unambiguous resonance assignments in nucleic acids following site-specific fully 15N,13C isotope incorporation at very low levels. The J-couplings between heteronuclei provide for distinction between the NMR signals of the fully labeled nucleotides and those of the natural abundance nucleotides. The method is demonstrated for DNA oligonucleotides, in the dimeric G-quadruplex [d(GGGTTCAGG)]2 and in the 22-nucleotide human telomeric fragment d[AG3(TTAG3)3]. We expect this approach to be useful for selective monitoring of important functional domains and of their interactions in large nucleic acids.

Carbon Isotopes↗
PubMed2003

K+ and Na+-induced self-assembly of telomeric oligonucleotide d(TTAGGG)n.

The telomeric DNA oligomers, d(TTAGGG)(n), where n=1, 2, 4, could self-associate into the multi-stranded structures in appropriate condition, exhibited different CD spectra. The presense of Na(+) was more advantage to facilitate the formation of anti-parallel conformation, but the presense of K(+) enhanced their thermal stability. Spectroscopic analysis of 3, 3'-diethyloxadicarbocyanine (DODC) showed the formation of hairpin quadruplex structures for d(TTAGGG)(2) and d(TTAGGG)(4), but d(TTAGGG) could not. The four-stranded tetraplexes and branched nanowire formed in the presense of K(+) or Na(+) alone were observed by atomic force microscopy (AFM). The ability of d(TTAGGG)(n) to self-assemble into four-stranded tetraplexes and nanowires depends strongly on the number of repeating units and ionic environment. A model to explain how these structures formed is proposed.

Cations, Monovalent↗
PubMed2002

Distinct domains in the CArG-box binding factor A destabilize tetraplex forms of the fragile X expanded sequence d(CGG)n.

Formation of hairpin or tetraplex structures of the FMR1 gene d(CGG)n sequence triggers its expansion, setting off fragile X syndrome. In searching for proteins that destabilize d(CGG)n secondary structures we purified from rat liver quadruplex telomeric DNA binding protein 42 (qTBP42) that disrupts G'2 bimolecular tetraplex d(CGG)n while paradoxically stabilizing the G'2 structure of the telomeric sequence d(TTAGGG)n. Based on peptide sequence homology of qTBP42 and mouse CArG-box binding factor A (CBF-A), we provide direct evidence that recombinant CBF-A protein is physically and immunochemically indistinguishable from qTBP42 and that it too destabilizes G'2 d(CGG)n while stabilizing G'2 d(TTAGGG)n. We inquired whether CBF-A employs the same or different domains to differentially interact with G'2 d(CGG)n and G'2 d(TTAGGG)n. Mutant CBF-A proteins that lack each or combinations of its five conserved motifs: RNP1(1), RNP1(2), RNP2(1), RNP2(2) and ATP/GTP-binding box were tested for their G'2 d(CGG)n destabilization and G'2 d(TTAGGG)n stabilization activities. We find that either RNP1(1) or the ATP/GTP motifs are necessary and sufficient for G'2 d(CGG)n destabilization whereas RNP2(1) suppresses destabilization by either one of these two motifs. Neither RNP1(1) nor the ATP/GTP motif are required for G'2 d(TTAGGG)n stabilization. Hence, CBF-A employs different domains to destabilize G'2 d(CGG)n or stabilize G'2 d(TTAGGG)n.

Animals↗
PubMed2002

G-quartets assembly within a G-rich DNA flap. A possible event at the center of the HIV-1 genome.

Stretches of guanines can associate in vitro through Hoogsteen hydrogen bonding to form four-stranded structures. In the HIV-1 central DNA flap, generated by reverse transcriptase at the end of retrotranscription, both the two 99 nt-long overlapping (+) strands contain two adjacent tracts of guanines. This study demonstrates that oligonucleotides containing these G-clusters form highly stable G-quadruplexes of various structures in vitro, whose formation was controlled by an easy and reversible protocol using sodium hydroxide. Among these sequences, a G'2 hairpin dimer was the most stable structure adopted by the 5'-tail of the (+) downstream strand. Since the two (+) strands of the HIV-1 central DNA flap hold these G-clusters, and based on the properties of reverse branch migration in DNA flaps, constructions using HIV-1 sequences were assembled to mimic small DNA flaps where the G-clusters are neighbors. G-quartets were successfully probed in such flaps. They were induced by potassium and by a dibenzophenanthroline derivative already known to stabilize them. Such results suggest some function(s) for G-quartets associated with a DNA flap in the HIV-1 pre-integration steps, and argue for their transient formation during the processing of G-rich DNA flaps at the time of replication and/or repair.

DNA↗
PubMed2003

Selective inhibitory DNA aptamers of the human RNase H1.

Human RNase H1 binds double-stranded RNA via its N-terminal domain and RNA-DNA hybrid via its C-terminal RNase H domain, the latter being closely related to Escherichia coli RNase HI. Using SELEX, we have generated a set of DNA sequences that can bind efficiently (K(d) values ranging from 10 to 80 nM) to the human RNase H1. None of them could fold into a simple perfect double-stranded DNA hairpin confirming that double-stranded DNA does not constitute a trivial ligand for the enzyme. Only two of the 37 DNA aptamers selected were inhibitors of human RNase H1 activity. The two inhibitory oligomers, V-2 and VI-2, were quite different in structure with V-2 folding into a large, imperfect but stable hairpin loop. The VI-2 structure consists of a central region unimolecular quadruplex formed by stacking of two guanine quartets flanked by the 5' and 3' tails that form a stem of six base pairs. Base pairing between the 5' and 3' tails appears crucial for conferring the inhibitory properties to the aptamer. Finally, the inhibitory aptamers were capable of completely abolishing the action of an antisense oligonucleotide in a rabbit reticulocyte lysate supplemented with human RNase H1, with IC50 ranging from 50 to 100 nM.

Animals↗
PubMed2004

Optical absorption assay for strand-exchange reactions in unlabeled nucleic acids.

The nucleic acid exchange reaction is a common feature for genetic recombination, DNA replication and transcription. Due to the fact that in the strand-exchange reactions the reactant and product molecules have similar or identical nucleotide sequences, the reaction is undetectable. As a rule, the nucleic acids with radioactive or fluorescence labels are used in such studies. Besides the fact that the labels can perturb the reaction and pose a health risk to the investigators, the assays usually involve extra experimental steps: quenching the reaction, separation, visualization and quantification of the products. Here, we describe a straightforward, direct and precise method to study strand-exchange reaction of unlabeled nucleic acids by real-time measurements of optical absorption. The method takes advantage of the property of some guanine-rich oligonucleotides to adopt monomolecular quadruplex conformation in the presence of certain cations. The conformation is characterized by significant absorption in long-wavelength range of the ultraviolet region where usually other secondary structures are transparent. The 'signal' oligonucleotide is incorporated into reactant duplex by annealing with target sequence. Adding the replacement sequence initiates the release of the 'signal' oligonucleotide into solution, which is accompanied by ultraviolet absorption in long-wavelength range.

Aptamers, Nucleotide↗
PubMed2005

Structural switch of telomere DNA by pH and monovalent cation.

Because of the importance of telomere DNAs, the structures of these DNAs in vivo and in vitro are currently of great research interest in the medical, pharmaceutical, chemical, and industrial fields. In this study, we investigated the structure and thermodynamic properties of the telomere DNAs in the presence of monovalent cations, K+ or Na+. The results demonstrate that the duplex-quadruplex conversion of the 1:1 mixture of telomere G-rich and C-rich sequences can be induced depending on cation species and its concentration. Furthermore, slightly acidic condition stabilizes the i-motif and forces the mixture to dissociate. These results suggest that the structure and stability of telomere DNAs can be controlled by monovalent cation and pH.

Cations, Monovalent↗