Polynucleotides, single-stranded, poly

Using enzymatic methods with the substrate ADP, it has been possible to prepare a single-stranded polynucleotide containing only one kind of base, known as poly A . Similarly with UDP, single-stranded poly U has been synthesised. If dilute solutions of poly A and poly U are mixed, hydrogen bonding between the different chains takes place and a synthetic donble-stranded specimen is obtained (Figure 10.51). 

A well-extended single-stranded polynucleotide, poly(A)... 

The study demonstrated that single-stranded polynucleotide, such as poly(A), is more flexible than a generic dsDNA. On mica, the long B-DNA binds to mica at many sites and remains intact during drying, while the short DNA binds at fewer sites and settles to an A-DNA structure during dehydration. 

Michaels HB, Hunt JW (1977a) Radiolysis of the double-stranded polynucleotides poly(A+U) and DNA in the presence of oxygen. Radiat Res 72 32-47 Michaels HB, Hunt JW (1977b) Reaction of oxygen with radiation-induced free radicals on single-stranded polynucleotides. Radiat Res 72 18-31... 

Sakurai K, Mizu M, Shinkai S (2001) Polysaccharide-polynucleotide complexes. 2. Complementary polynucleotide mimic behavior of a natural polysaccharide schizophyllan in the macromolecular comple with a single strand RNA poly(C). Biomacromolecules 2 641-650... 

Double helical structures may be constructed from complementary single-stranded polynucleotide chains sharing a common helical axis according to the procedure outlined below. The two strands of the complex are assumed to be regular helices defined by a common set of backbone and glycosyl torsion angles. The data presented here are limited to model poly(dA) poly(dT) double helices stabilized by Watson-Crick base pairs between anti parallel strands. 

One well-established observation is that, under conditions where single-stranded polynucleotides give rise to a d.c. polarographic reduction wave, both native DNA and other double-helical natural and synthetic polynucleotides are inactive 22 23,46-47, 58,59,61) Tjjjs js rea(ji]y interpretable in that, in such helical structures, the adenine and cytosine residues are located in the interior of the helix, and hydrogen bonded in complementary base pairs (see below). Z-DNA, in which cytosine residues are at the surface of the helix, is of obvious interest in this regard, and the B - Z transition in the synthetic poly(dG dC) has been investigated with the aid of differential pulse polarography and UV spectroscopy 60). 

The density, p, of a double stranded DNA molecule, and hence its position in the gradient, depends primarily on its nucleotide composition (eq. 2.2 gives p= 1.660+0.098 (GC)). The relation does not hold for DNAs containing glucosylated, methylated or other modified residues, nor for DNAs of very simple sequence such as synthetic polynucleotides, crab poly dAT (Wells et al. 1970) and centromeric DNA. Single stranded DNA is denser than double stranded DNA and isopycnic centrifugation can be used to separate them. 

The two types of natural polynucleotides (nucleic acids) are classified according to the sugars they contain. Ribonucleic acid (RNA) contains exclusively P-o-ribose, while the sugar in deoxyribonucleic acid (DNA) is P-2-deoxy-D-ribose. Different nucleic acids can have from around 80 nucleotides (nt), as in transfer RNA (tRNA), to over 10 nucleotide-pairs in a single eukaryotic chromosome. The unit for size of nucleic acid is the base (for single-stranded species) or the base-pair (bp, for double-stranded species), with the unit Kb (thousand base-pairs) and Mb (million base-pairs). Examples of synthetic homopolynucleotides are poly(uridylate) or poly(deoxyadenylate), in poly(U) or poly(dA)... 

PARR poly(ADP-ribose) polymerase XRCCl, X-ray cross complementing faaor 1 BRCT, BRCAl c-terminus UVDE, UV damage endonuclease GFP, green fluorescent protein 3-AB, 3-aminobenzamide XPA, xeroderma pigmentosum group A DAPI, 4, 6-diamidino-2-phenylindol TDT, deoxynucleotidyl transferase PNK, polynucleotide kinase MEFs, mouse embryonic fibroblasts SSB, single strand breaks SSBR, single strand breaks repair DSB, double strand breaks. 

Recently, we found that when certain single-stranded polynucleotides such as poly(5 -cytidine monophosphate), denoted by poly(C), coexists in the renature process of P-(1 3)-glucans mentioned above, the polynucleotide and s-SPG form a macromolecular complex.Our subsequent studies show that this complexa-tion is a characteristic nature commonly observed for all P-(1 3)-glucans. As far as we know, this is the first study showing that a neutral polysaccharide can combine with polynucleotides. If s-SPG can enter a cancer cell and combine with... 

Calf thymus DNA, Xenopus liver DNA, and also DNA from T4 coli phage inhibit the vegetalizing factor. Heteropolymeric [poly d( A-T), poly d(G-C), poly d(I-C)] and homopolymeric (poly I-poly C, poly dA poly dT) double-stranded polynucleotides have no inhibitory activity (Table I). Melted, single-stranded chick DNA has about the same inhibitory effect as double-stranded DNA. However, it is not excluded that a partial renaturation occurs under the conditions of the test. Also, DNA, which was partially degraded by sonication, has about the same inhibitory effect as untreated DNA. 

Synthetic polynucleotide complexes have been shown to be effective immune response modulators in animals and man (Braun et al. 1971, Johnson 1979). The polynucleotides are formed foUowing the action of an enzyme, polynucleotide phosphor-ylase on the synthetic mononucleotide diphosphates. Complexing takes place following the mixing of polymers composed of opposite base pairs. Two have been utilised, polyinosinic acid complexed with polycytidylic acid (poly I poly C) and polyad-enylic acid complexed with polyuridylic acid (poly A poly U). The single strands mononucleotides are ineffective. 

Template-induced polymerization of nucleotides. The idea is to have one single-stranded polynucleotide (e.g. poly A) as guest in reverse micelles, as well as an excess of mononucleotide (e. g. U or of short oligomers thereof). The binding A=U should produce an array of U lined up to the poly A matrix, and the polymerization should then take place by chemical activation. The process, if successful, can lead to any series of block copolymers or random copolymers. 

The preceding considerations, together with others drawn from the results of model building studies and from an analysis of the substrate specificity of pancreatic RNase (v. infra) are discussed more fully elsewhere all are consistent with the following formulations in contrast to normal nucleotides (1) formycin residues in polynucleotides are subject to conformational transitions which tcike place at the glycosyl bond. (2) The formycin nucleotides are (a) anti in ordered double-stranded structures of the Watson-Crick type (b) syn in neutral poly F and (c) probably a mixture of syn and anti in single stranded copolymers. 

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