Double-stranded complexes, poly

A (Scheme 1) was also reported to form complexes with poly(uridylic acid) [poly(U)j. Due to the shorter distance between adenines in 2A compared with that of poly(U), the complexes were proposed to be 2 poly(U)-2A triple-stranded, poly(U)-2A double-stranded, and poly(U)-25% adenine of 2A double-stranded [46]. 

Several additional results have arisen from these studies. Polynucleotides can not only form Watson-Crick helical double-stranded complexes but may also form helical structures between themselves which can have more than two strands, as well as non-Watson-Crick base pairs, like the complex poly(l) poly(A)-poly(l). Furthermore, numerous polymers of base and sugar analogues have been prepared and studied. 

In aqueous solution the two homopolynucleotides poly I and poly C readily associate to give a double hehcal complex poly I poly C (Davies and Rich, 1958). The stoichiometry of this complex has been estabUshed by a variety of techniques and at pH 7 only the double-stranded complex is obtained. No triple-stranded structure has been demonstrated under these conditions. The stabihty of the complex is a function of salt concentration and in 0.15 MNa+, pH 7.0, the temperature of dissociation of the two strands is about 60°. The complex is a right-handed hehx and appears to have a geometry similar to that of the A form of RNA. 

The double helical complex poly A poly U adsorbed onto MBSA has been used as immunogen in Fauve de Bourgogne rabbits (Nahon et al., I967) and in New Zealand White rabbits (Schwartz and Stollar, 1969). In both cases antibodies reacting specifically with poly A poly U were induced. These antibodies react also with the heterologous double-helical complex poly I poly C although they do not react with the separate homopolyribonucleotides poly I or poly C. In addition, the reaction is abolished if the complex is heated in the presence of formaldehyde. It is thus possible to conclude that these antibodies are specific for the double-stranded structure. 

In fact, all of the heterologous double-stranded complexes which have been tested react to different extents with anti-poly A poly U antibodies. Among these complexes, poly rG poly rC precipitates the smallest amount of antibodies and the reactivity differs not only from that of poly rl poly rC but also from that of the equivalent double-helical polydeoxyribonucleotide complex containing guanine and cytosine residues, poly dG - poly dC (Fig. 5). Thus the homologous antigen precipitates 219.7 [xg/ml of antibodies (expressed as N), poly rl poly rC precipitates almost the same amount, 209.5 (J-g/ml, and poly rG poly rC precipitates only 20.3 [xg/ml, whereas poly dG poly dC shows an intermediate reactivity and precipitates 77.8 (xg/ml of antibodies of the same anti-poly A poly U serum. 

CNTs can conjugate with nucleic acids via non-covalent bond. ssDNA, short double-stranded DNA and total RNA molecules can attach to the surface of CNTs and can disperse CNTs in aqueous environment. The poly(30T) has the highest dispersion efficiency (Zheng et al., 2003). For example, 1 mg DNA molecules mix with lmg CNTs in 1ml water, yield at most 4mg/ml CNT solution. DNA-CNT complexes can be purified or isolated by electronic properties such as agarose gel electrophoresis and centrifuge method (Cui et al., 2004a Karajanagi et al., 2004). 

For the complexation of double-stranded DNA, a more elaborate polynucleotide morphology has been designed via the introduction of homopolynucleotide sequences on the ends for SPG binding [54]. Poly(dA) 80-mer was introduced at both ends of DNA, forming loops which provide protection from degradation by endonucleases, an approach adopted from viruses. 

The distortions induced in the DNA double helix by the interstrand cross-links have been characterized by several techniques. As judged by chemical probes (diethyl pyrocarbonate, hydroxylamine, osmium tetroxide), antibodies to cisplatin-modified poly(dG-dC)-poly(dG-dC), natural (DNase I) and artificial (1,10-phenanthroline-copper complex) nucleases, the cytosine residues are accessible to the solvent, and the distortions are located at the level of the adduct [48-50]. From the electrophoretic mobility of the multimers of double-stranded oligonucleotides containing a single interstrand cross-link [50] it is deduced that the DNA double helix is unwound (79°) and its axis is bent (45°). 

An ESI mass spectrum of a mixture of 1 1 d(pT)13 d(pA)14 with the gene V protein (Fig. 13a) shows the existence of a double-stranded dimer and of a complex between the protein and a single d(pT)13 oligonucleotide. Complexes of the protein with the dsDNA, or with d(pA)14 do not appear in the spectrum. This clearly points to the preference for binding ssDNA over dsDNA and poly(dT) over polyfdA). When the mixture of d(pT)13 d(pT)15 ... 

Poly-VAd can form polymer complexes with poly-VUr8 or with poly(uridylic acid)-(poly U)8 16. The formation of triple-stranded (2 poly U poly-VAd) and double-stranded (poly U poly-VAd) structures containing poly-VAd loops were proposed for the poly U poly-VAd system16. The formation of these complexes seems to depend on the reaction condition. 

One can differentiate two main methods for obtaining polymer-polymer complexes 1) formation of complexes from pre-existing chemically and structurally complementary macromolecules 2) polymerization of monomers in the presence of matrix macromolecules introduced in the reaction media. Such matrix polymerization is accompanied by the formation of polymer complexes. In the first case, the chemical reaction proceeds via complex formation by random contacts between reacting chains. Then, these sequences of pairs of connected chains grow. In matrix polymerization, the complex is formed by the mechanism of consecutive addition of monomer along the chain leading to the formation of the so-called zip-up (double-stranded) structure, due to matrix control of polymerization. One can expect that the various mechanisms lead to the formation of complexes with a different structure and properties. Indeed, a difference in the composition and properties of complexes obtained by various methods has been found So, the comparison of complexes poly(methacry-lic acid)-poly(2-N,N-dimethylaminoethyl methacrylate), obtained by mixing of equimolar quantities of components in solution and also by the matrix polymerization of dimethylaminoethyl methacrylate in water in the presence of PMAA, shows a difference in composition. In the first case, the content of acid in the complex is always... 

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