DNA hairpin

We report the conformational restriction of a freely rotating biaryl derivative resulting in strong exciton coupled circular dichroism between the two nondegenerate fragments of the dyad NP only in the presence of DNA. The napthalenimide-perylenimide dyad NP, an extended 1,1′-binaphthalene derivative, has a rotational barrier of 100 kJ/mol, leading to fast racemization. While end-stacking with a DNA hairpin, NP exhibits a significantly high rotational barrier, an additional 91 kJ/mol, resulting in atroposelective preference. Such reversible conformational constraints using biotemplates show huge potential toward conformational analysis, dynamic kinetic resolution, and asymmetric synthesis. The present work focuses on conformational analysis of a freely rotating biaryl derivative using a combination of techniques such as temperature-dependent UV-vis, circular dichroism, steady-state and time-resolved fluorescence spectroscopy, and molecular dynamics simulation.

The physical properties of the D N A oligomer d(CGCGCGTTTTCGCGCG) in solvents containing 4 M NaC104 and 0.1 M NaCl were investigated by proton NMR, optical melting, and circular dichroism spectroscopy. Results of these investigations are as follows: (i) The D N A hexadecamer exists as a unimolecular hairpin in either high or low salt. (ii) In high salt the stem region of the hairpin is in the left-handed Z conformation. (iii) In either high or low salt, the duplex stem of the hairpin is stabilized against melting by-40 OC compared to the linear core duplex. The added stability of the hairpin is entropic in origin. (iv) In high salt, as the temperature is elevated, the equilibrium structure of the duplex stem +This work was supported by NIH Grant GM39471 (A.S.B. and M.A.), Illinois Division of the American Cancer Society Grant 87-30 (Y.W. and S I .) , and the Research Corporation (S I .

Conformational polymorphism of DNA is a major causative factor behind several incurable trinucleotide repeat expansion disorders that arise from overexpansion of trinucleotide repeats located in coding/non-coding regions of specific genes. Hairpin DNA structures that are formed due to overexpansion of CAG repeat lead to Huntington's disorder and spinocerebellar ataxias. Nonetheless, DNA hairpin stem structure that generally embraces B-form with canonical base pairs is poorly understood in the context of periodic noncanonical A…A mismatch as found in CAG repeat overexpansion. Molecular dynamics simulations on DNA hairpin stems containing A…A mismatches in a CAG repeat overexpansion show that A…A dictates local Z-form irrespective of starting glycosyl conformation, in sharp contrast to canonical DNA duplex. Transition from B-to-Z is due to the mechanistic effect that originates from its pronounced nonisostericity with flanking canonical base pairs facilitated by base extrusion, ba...

Structural polymorphism of DNA has constantly been evolving from the time of illustration of the double helical model of DNA by Watson and Crick. A variety of non-canonical DNA structures have constantly been documented across the globe. DNA attracted worldwide attention as a carrier of genetic information. In addition to the classical Watson-Crick duplex, DNA can actually adopt diverse structures during its active participation in cellular processes like replication, transcription, recombination and repair. Structures like hairpin, cruciform, triplex, G-triplex, quadruplex, i-motif and other alternative non-canonical DNA structures have been studied at length and have also shown their in vivo occurrence. This review mainly focuses on non-canonical structures adopted by DNA oligonucleotides which have certain prerequisites for their formation in terms of sequence, its length, number and orientation of strands along with varied solution conditions. This conformational polymorphism of DNA might be the basis of different functional properties of a specific set of DNA sequences, further giving some insights for various extremely complicated biological phenomena. Many of these structures have already shown their linkages with diseases like cancer and genetic disorders, hence making them an extremely striking target for structure-specific drug designing and therapeutic applications.

Conformational polymorphism of DNA is a major causative factor behind several incurable trinucleotide repeat expansion disorders that arise from overexpansion of trinucleotide repeats located in coding/non-coding regions of specific genes. Hairpin DNA structures that are formed due to overexpansion of CAG repeat lead to Huntington's disorder and spinocerebellar ataxias. Nonetheless, DNA hairpin stem structure that generally embraces B-form with canonical base pairs is poorly understood in the context of periodic noncanonical A…A mismatch as found in CAG repeat overexpansion. Molecular dynamics simulations on DNA hairpin stems containing A…A mismatches in a CAG repeat overexpansion show that A…A dictates local Z-form irrespective of starting glycosyl conformation, in sharp contrast to canonical DNA duplex. Transition from B-to-Z is due to the mechanistic effect that originates from its pronounced nonisostericity with flanking canonical base pairs facilitated by base extrusion, ba...

Conformational polymorphism of DNA is a major causative factor behind several incurable trinucleotide repeat expansion disorders that arise from overexpansion of trinucleotide repeats located in coding/non-coding regions of specific genes. Hairpin DNA structures that are formed due to overexpansion of CAG repeat lead to Huntington's disorder and spinocerebellar ataxias. Nonetheless, DNA hairpin stem structure that generally embraces B-form with canonical base pairs is poorly understood in the context of periodic noncanonical A…A mismatch as found in CAG repeat overexpansion. Molecular dynamics simulations on DNA hairpin stems containing A…A mismatches in a CAG repeat overexpansion show that A…A dictates local Z-form irrespective of starting glycosyl conformation, in sharp contrast to canonical DNA duplex. Transition from B-to-Z is due to the mechanistic effect that originates from its pronounced nonisostericity with flanking canonical base pairs facilitated by base extrusion, ba...

Quasi-palindromic sequences (AT) X N 12 (AT) Y present in HS2 (hypersensitive site) of the human β-globin locus are known to be significantly associated with increased fetal hemoglobin (HbF) levels. High HbF levels in some adults arise due to pathological conditions such as sickle cell disease and β-thalassemia. However, elevated levels of HbF are also associated with a reducing morbidity and mortality in patients with β-thalassemia and thus ameliorate the severity of the disease. Using gel-electrophoresis, ultraviolet (UV)thermal denaturation and circular dichroism (CD) techniques, we demonstrated that it exhibits a hairpin-duplex equilibrium. Intramolecular species (hairpin) were observed in both low as well as high salt concentration in gel assay studies displaying the unusual stability of intramolecular species even at the high counter-ion concentration. Unusual stability of hairpin secondary structures was also demonstrated by the monophasic nature of the melting profiles for the oligonucleotides which persisted at low as well as high salt and oligomer concentrations. Change in CD spectra as a function of oligomer concentration indicates that the bimolecular duplex formation is selectively favored over monomolecular hairpin formation at and above 9 µM oligomer concentration. Thus, we hypothesize that imperfect inverted repeat sequence (AT) X N 12 (AT) Y of HS2 of β-globin gene LCR form the unusually stable hairpins which may result in the formation of a cruciform structure that may be recruited for binding by various nuclear proteins that could result in elevated HbF levels.

Structural polymorphism of DNA has constantly been evolving from the time of illustration of the double helical model of DNA by Watson and Crick. A variety of non-canonical DNA structures have constantly been documented across the globe. DNA attracted worldwide attention as a carrier of genetic information. In addition to the classical Watson-Crick duplex, DNA can actually adopt diverse structures during its active participation in cellular processes like replication, transcription, recombination and repair. Structures like hairpin, cruciform, triplex, G-triplex, quadruplex, i-motif and other alternative non-canonical DNA structures have been studied at length and have also shown their in vivo occurrence. This review mainly focuses on non-canonical structures adopted by DNA oligonucleotides which have certain prerequisites for their formation in terms of sequence, its length, number and orientation of strands along with varied solution conditions. This conformational polymorphism of DNA might be the basis of different functional properties of a specific set of DNA sequences, further giving some insights for various extremely complicated biological phenomena. Many of these structures have already shown their linkages with diseases like cancer and genetic disorders, hence making them an extremely striking target for structure-specific drug designing and therapeutic applications.

Repetitive DNA sequences are ubiquitous in life, and changes in the number of repeats often have various physiological and pathological implications. DNA repeats are capable of interchanging between different noncanonical and canonical conformations in a dynamic fashion, causing configurational slippage that often leads to repeat expansion associated with neurological diseases. In this report, we used single-molecule spectroscopy together with biophysical analyses to demonstrate the parity-dependent hairpin structural polymorphism of TGGAA repeat DNA. We found that the DNA adopted two configurations depending on the repeat number parity (even or odd). Transitions between these two configurations were also observed for longer repeats. In addition, the ability to modulate this transition was found to be enhanced by divalent ions. Based on the atomic structure, we propose a local seeding model where the kinked GGA motifs in the stem region of TGGAA repeat DNA act as hot spots to facili...

Single-stranded DNA or double-stranded DNA has the potential to adopt a wide variety of unusual duplex and hairpin motifs in the presence (trans) or absence (cis) of ligands. Several principles for the formation of those unusual structures have been established through the observation of a number of recurring structural motifs associated with different sequences. These include: (i) internal loops of consecutive mismatches can occur in a B-DNA duplex when sheared base pairs are adjacent to each other to confer extensive cross-and intra-strand base stacking; (ii) interdigitated (zipper-like) duplex structures form instead when sheared G´A base pairs are separated by one or two pairs of purine´purine mismatches; (iii) stacking is not restricted to base, deoxyribose also exhibits the potential to do so; (iv) canonical G´C or A´T base pairs are¯exible enough to exhibit considerable changes from the regular H-bonded conformation. The paired bases become stacked when bracketed by sheared G´A base pairs, or become extruded out and perpendicular to their neighboring bases in the presence of interacting drugs; (v) the purine-rich and pyrimidine-rich loop structures are notably different in nature. The purinerich loops form compact triloop structures closed by a sheared G´A, A´A, A´C or sheared-like G anti´Csyn base pair that is stacked by a single residue. On the other hand, the pyrimidine-rich loops with a thymidine in the ®rst position exhibit no base pairing but are characterized by the folding of the thymidine residue into the minor groove to form a compact loop structure. Identi®cation of such diverse duplex or hairpin motifs greatly enlarges the repertoire for unusual DNA structural formation.

Single-stranded DNA or double-stranded DNA has the potential to adopt a wide variety of unusual duplex and hairpin motifs in the presence (trans) or absence (cis) of ligands. Several principles for the formation of those unusual structures have been established through the observation of a number of recurring structural motifs associated with different sequences. These include: (i) internal loops of consecutive mismatches can occur in a B-DNA duplex when sheared base pairs are adjacent to each other to confer extensive cross-and intra-strand base stacking; (ii) interdigitated (zipper-like) duplex structures form instead when sheared G´A base pairs are separated by one or two pairs of purine´purine mismatches; (iii) stacking is not restricted to base, deoxyribose also exhibits the potential to do so; (iv) canonical G´C or A´T base pairs are¯exible enough to exhibit considerable changes from the regular H-bonded conformation. The paired bases become stacked when bracketed by sheared G´A base pairs, or become extruded out and perpendicular to their neighboring bases in the presence of interacting drugs; (v) the purine-rich and pyrimidine-rich loop structures are notably different in nature. The purinerich loops form compact triloop structures closed by a sheared G´A, A´A, A´C or sheared-like G anti´Csyn base pair that is stacked by a single residue. On the other hand, the pyrimidine-rich loops with a thymidine in the ®rst position exhibit no base pairing but are characterized by the folding of the thymidine residue into the minor groove to form a compact loop structure. Identi®cation of such diverse duplex or hairpin motifs greatly enlarges the repertoire for unusual DNA structural formation.

Advances in Cyclic Voltammetry Voltammetry methods are simple, sensitive, selective and timesaving in nature [4]. Analytical properties are enhanced by combining voltammetry technique with several separation methods such as capillary electrophoresis, flow injection, and HPLC. Cyclic Voltammetry (CV) technique was developed in order to study the electron-transfer in conventional redox reactions of organic as well as inorganic chemistry, multi-electron transfer processes of biochemistry. Stability of reaction products, kinetics of electron-transfer, and involvement of

Structural polymorphism of DNA is a widely accepted property. A simple addition to this perception has been our recent finding, where a single nucleotide polymorphism (SNP) site present in a quasipalindromic sequence of b-globin LCR exhibited a hairpin-duplex equilibrium. Our current studies explore that secondary structures adopted by individual complementary strands compete with formation of a perfect duplex. Using gel-electrophoresis, ultraviolet (UV)-thermal denaturation, circular dichroism (CD) techniques, we have demonstrated the structural transitions within a perfect duplex containing 11 bp quasipalindromic stretch (TGGGG(G/C)CCCCA), to hairpins and bulge duplex forms. The extended version of the 11 bp duplex, flanked by 5 bp on both sides also demonstrated conformational equilibrium between duplex and hairpin species. Gel-electrophoresis confirms that the duplex coexists with hairpin and bulge duplex/ cruciform species. Further, in CD spectra of duplexes, presence of two overlapping positive peaks at 265 and 285 nm suggest the features of A-as well as B-type DNA conformation and show oligomer concentration dependence, manifested in A ! B transition. This indicates the possibility of an architectural switching at quasipalindromic region between linear duplex to a cruciform structure. Such DNA structural variations are likely to be found in the mechanics of molecular recognition and manipulation by proteins.

Some useful CD applications aiming to investigate the B-Z conformational change in nucleic acids as well as their inter actions with a ruthenium complex of potential terapeutic interest are described in this paper. The results presented here regard: a) the energetics of the conformational transition from the B right-handed to the Z left-handed helix in synthetic oligodeoxynucleotides with a cytosine-guanine alternating sequence; b) The B to Z transition for sequences containing all four canonical bases and the role of nickel ions and sodium perchlorate in promoting this tranformation; c) the inter action of Ru(II)(DMSO)4CI2. a compound exhibiting a good antitumor activity in animals, with both mononucleosides and polynucleotides.

We studied DNA dodecamers (CAG) 4 , (CCG) 4 , (CGG) 4 and (CTG) 4 by CD spectroscopy and polyacrylamide gel electrophoresis. Each dodecamer adopted several ordered conformers which denatured in a cooperative way. Stability of the conformers depended on the dodecamer concentration, ionic strength, temperature and pH. The dodecamers, having a pyrimidine base in the triplet center, generated foldbacks at low ionic strength whose stem conformations were governed by the GC pairs. At high salt, (CCG) 4 isomerized into a peculiar association of two strands. The association was also promoted by high oligonucleotide concentrations. No similar behavior was exhibited by (CTG) 4. At low salt, (CGG) 4 coexisted in two bimolecular conformers whose populations were strongly dependent on the ionic strength. In addition, (CGG) 4 associated into a tetraplex at acidic pH. A tetraplex was even observed at neutral pH if the (CGG) 4 concentration was sufficiently high. (CAG) 4 was very stable in a monomolecular conformer similar to the known extremely stable foldback of the (GCGAAGC) heptamer. Nevertheless, even this very stable conformer disappeared if (CTG) 4 was added to the solution of (CAG) 4. Association of the complementary strands was also strongly preferred to the particular strand conformations by the other couple, (CCG) 4 and (CGG) 4 .

Here we review studies that provided important information about conformational properties of DNA using circular dichroic (CD) spectroscopy. The conformational properties include the B-family of structures, A-form, Z-form, guanine quadruplexes, cytosine quadruplexes, triplexes and other less characterized structures. CD spectroscopy is extremely sensitive and relatively inexpensive. This fast and simple method can be used at low- as well as high-DNA concentrations and with short- as well as long-DNA molecules. The samples can easily be titrated with various agents to cause conformational isomerizations of DNA. The course of detected CD spectral changes makes possible to distinguish between gradual changes within a single DNA conformation and cooperative isomerizations between discrete structural states. It enables measuring kinetics of the appearance of particular conformers and determination of their thermodynamic parameters. In careful hands, CD spectroscopy is a valuable tool for mapping conformational properties of particular DNA molecules. Due to its numerous advantages, CD spectroscopy significantly participated in all basic conformational findings on DNA.

Repetitive DNA sequences are ubiquitous in life, and changes in the number of repeats often have various physiological and pathological implications. DNA repeats are capable of interchanging between different noncanonical and canonical conformations in a dynamic fashion, causing configurational slippage that often leads to repeat expansion associated with neurological diseases. In this report, we used single-molecule spectroscopy together with biophysical analyses to demonstrate the parity-dependent hairpin structural polymorphism of TGGAA repeat DNA. We found that the DNA adopted two configurations depending on the repeat number parity (even or odd). Transitions between these two configurations were also observed for longer repeats. In addition, the ability to modulate this transition was found to be enhanced by divalent ions. Based on the atomic structure, we propose a local seeding model where the kinked GGA motifs in the stem region of TGGAA repeat DNA act as hot spots to facili...

Conformational switching in DNA is fundamental to biological processes. The structural status of a palindromic GC-rich dodecamer DNA sequence, integral part of human MRC2 coding region, and a related sequence of opposite polarity from human FDX1 gene were characterized and compared. UV-melting, circular dichroism, and gel electrophoresis experiments demonstrated the formation of intermolecular structures. Although stability and molecularity of both the oligomeric structures were found to be almost identical, their secondary structures differed remarkably as A1 MRC2 sequence showed Alike and B-like DNA conformation, whereas the A2 FDX1 sequence exhibited only the Alike signatures. The study is relevant for understanding structural polymorphism at genomic locations depending on DNA sequence and solution environment.

DNA fragments containing the sequence d(GCGAAAGC) adopt a base-intercalated (zipper-like) duplex in crystalline state at high ionic strength. To investigate effects of point mutation at the 5th residue on the structure, two crystal structures of d(GCGAGAGC) and d(GCGATAGC) have been determined by X-ray crystallography. In both crystals, the two octamers related by a crystallographic two-fold symmetry are aligned in an anti-parallel fashion and associated to each other to form a duplex, suggesting that the base-intercalated duplex is stable even when the 5th residue is mutated with other bases. The sheared G3:A6 pair formation makes the two phosphate backbones closer and facilitates formation of the A-X*-X-A* base-intercalated motif. The three duplexes are assembled around the two hexamine cobalt chlorides. The central X and X* residues are bound to a different cation depending on the kinds of bases.

Nucleic acids can undergo dynamic conformational changes associated with the regulation of biological processes. A molecule presenting larger affinities for alternative structures relative to a duplex is expected to modify such conformational equilibria. We have previously reported that macrocyclic bis-acridine binds preferentially to single-stranded regions, especially DNA hairpins, due to steric effects. Here, we show, using gel electrophoresis, fluorescence and melting temperature experiments, that the macrocycle bis-acridine shifts an equilibrium from a duplex towards the corresponding hairpins. Competition experiments enlighten the higher affinity of the macrocycle for hairpins compared with double-stranded DNA. The macrocycle bis-acridine destabilizes a synthetic polynucleotide, by the formation of premelted areas. By extrapolation, the macrocycle bis-acridine should be able to disrupt, at least locally, genomic DNA duplexes and to stabilize unpaired areas, especially palindromic ones forming hairpins. Such macrocyclic compounds may have potential applications in the therapy of diseases involving hairpins.

Structural polymorphism of DNA has constantly been evolving from the time of illustration of the double helical model of DNA by Watson and Crick. A variety of non-canonical DNA structures have constantly been documented across the globe. DNA attracted worldwide attention as a carrier of genetic information. In addition to the classical Watson-Crick duplex, DNA can actually adopt diverse structures during its active participation in cellular processes like replication, transcription, recombination and repair. Structures like hairpin, cruciform, triplex, G-triplex, quadruplex, i-motif and other alternative non-canonical DNA structures have been studied at length and have also shown their in vivo occurrence. This review mainly focuses on non-canonical structures adopted by DNA oligonucleotides which have certain prerequisites for their formation in terms of sequence, its length, number and orientation of strands along with varied solution conditions. This conformational polymorphism of DNA might be the basis of different functional properties of a specific set of DNA sequences, further giving some insights for various extremely complicated biological phenomena. Many of these structures have already shown their linkages with diseases like cancer and genetic disorders, hence making them an extremely striking target for structure-specific drug designing and therapeutic applications.

Structural polymorphism of DNA has constantly been evolving from the time of illustration of the double helical model of DNA by Watson and Crick. A variety of non-canonical DNA structures have constantly been documented across the globe. DNA attracted worldwide attention as a carrier of genetic information. In addition to the classical Watson-Crick duplex, DNA can actually adopt diverse structures during its active participation in cellular processes like replication, transcription, recombination and repair. Structures like hairpin, cruciform, triplex, G-triplex, quadruplex, i-motif and other alternative non-canonical DNA structures have been studied at length and have also shown their in vivo occurrence. This review mainly focuses on non-canonical structures adopted by DNA oligonucleotides which have certain prerequisites for their formation in terms of sequence, its length, number and orientation of strands along with varied solution conditions. This conformational polymorphism of...

A gradual dementia, which leads to the loss of memory and intellectual abilities, is the main characteristics of Alzheimer's disease. Amyloid-β (Aβ) plaques are the main components that accumulate and form clumps in the brains of people suffering from Alzheimer's disease. Apolipoprotein E (), an amyloid-binding protein is considered as one of the main genetic risk factor of the late-onset Alzheimer's disease. Different isoforms of gene named APOE2, APOE3, and APOE4 are known to exist, which differ from each other at certain positions involving single-nucleotide polymorphisms (SNPs). Out of these isoforms, APOE4 increases the risk of developing late-onset Alzheimer's disease, whereas APOE3 is the most common among the general population. APOE4 differs from the common APOE3 by only one nucleotide at position +2985 (T to C), which results in immense alteration in the structure and function of the gene. A combination of gel electrophoresis (polyacrylamide gel electrophor...

Our recent work on an AfiG single nucleotide poly- morphism (SNP) at the quasi-palindromic sequence d(TGGGG(A/G)CCCCA) of HS4 of the human b-globin locus control region in an Indian popula- tion showed a significant association between the G allele and the occurrence of b-thalassemia. Using UV-thermal denaturation, gel assay, circular dichro- ism (CD) and nuclease digestion experiments we have demonstrated that

Triplex nucleic acid structures receive considerable attention due to their possible role in anti-gene therapy, several diseases as Friedreich's ataxia and Deoxyribonucleic acid (DNA) based nano-structures. The modulation of triplex formation and its stabilization using small molecules is one way to enhance their utility in such applications. Here, we synthesized five new Azacyanines (Azaethyl (2 b), Azapropyl (2 c), Azaisopropyl (2 d), Azabutyl (2 e), Azaisobutyl (2 f)) and assessed their affinity and selectivity towards polyd(A), polyd(T), polyd(A)⋅polyd(T) and polyd(A)⋅polyd(T)⋅polyd(T) along with the previously synthesized Azamethyl (2 a). Our UV-Vis, CD and competition dialysis results revealed that Azacyanines were selective towards polyd (A)⋅polyd(T)⋅polyd(T) triplex. They were stabilizing triplex structure to different degrees, the degree of stabilization being dependent on the alkyl chain length and branching on the benzimidazole ring. Thermal denaturation temperature of the triplex in the presence of Azacyanines was increasing in order: Azamethyl (2 a) > Azaethyl (2 b) > Azapropyl (2 c) > Azabutyl (2 e) > Azaisobutyl (2 f) > Azaisopropyl (2 d). Our results also demonstrate that, Azamethyl (2 a) was able to disproportionate polyd(A)⋅polyd(T) into intercalated polyd(A)⋅polyd(T)⋅polyd(T) complex.

The NF-U UB transcriptional factor regulates various functions such as immune responses, cellular growth and development, and is frequently activated in tumor cells. Thus, inhibition of NF-U UB could suppress tumor cell growth. Using a decoy synthetic hairpin-shaped oligodeoxyribonucleotide (ODN) containing the U UB site with an integrated single diphos-phoryldisul¢de linkage, we demonstrate its covalent binding to the p50 subunit of NF-U UB. Furthermore, this decoy ODN induces apoptosis in a lymphoblastoma cell line. Thus, such chemically modi¢ed decoys could be valuable tools for blocking nuclear factors and tumor cell growth.

Background: The transcription factor STAT3 (signal transducer and activator of transcription 3) is frequently activated in tumor cells. Activated STAT3 forms homodimers, or heterodimers with other TFs such as NF-B, which becomes activated. Cytoplasmic STAT3 dimers are activated by tyrosine phosphorylation; they interact with importins via a nuclear localization signal (NLS) one of which is located within the DNA-binding domain formed by the dimer. In the nucleus, STAT3 regulates target gene expression by binding a consensus sequence within the promoter. STAT3-specific decoy oligonucleotides (STAT3-decoy ODN) that contain this consensus sequence inhibit the transcriptional activity of STAT3, leading to cell death; however, their mechanism of action is unclear.

The NF-U UB transcriptional factor regulates various functions such as immune responses, cellular growth and development, and is frequently activated in tumor cells. Thus, inhibition of NF-U UB could suppress tumor cell growth. Using a decoy synthetic hairpin-shaped oligodeoxyribonucleotide (ODN) containing the U UB site with an integrated single diphos-phoryldisul¢de linkage, we demonstrate its covalent binding to the p50 subunit of NF-U UB. Furthermore, this decoy ODN induces apoptosis in a lymphoblastoma cell line. Thus, such chemically modi¢ed decoys could be valuable tools for blocking nuclear factors and tumor cell growth.

Irradiation, with 350 nm UV light, of specially designed and synthesized single-and double-stranded oligodeoxyribonucleotides in the presence of 3-(p-tolylamino)-1,5-azulenequinone produced fragments resulting from the cleavage at the deoxyguanosine residue only. The cleaving efficiency was greater for a single strand than a double helix. The efficiency was increased for a less stable double helix, or while the deoxyguanosine residue therein was located at a bulge, at a hairpin loop, or towards the end of the helix.