Polynucleotide triple-helical

A few recent NMR investigations of polynucleotides include studies of triple-helical DNA,689 Holliday junctions,290 double-stranded oligonucleotides containing adducts of carcinogens,690 691 of hairpin loops with sheared A A and G G pairs,692 and of proton exchange in both imino and amino groups.693... 

Antibodies specific for triple-helical polynucleotides clearly distin-... 

Polynucleotides were reported to form triple helices as early as 1957. Triple strands can form by non-Watson-Crick hydrogen bonds between the third strand and purines involved in Watson-Crick hydrogen bonding with the complementary strand of the duplex (for review, see Ref 34). Thus, triple-stranded structures can be formed between a third strand composed of pyrimidines or purines that interact with a homopurine strand in a homopurine-homopyrimidine strand in a duplex DNA. With the demonstration that homopyrimidine oligonucleotides could indeed form triplex structures (35-37), interest in triple-strand approaches to inhibit transcription heightened. 

Figure 4. Diffraction from a screw-disordered" arrangement of poly U poly A poly U molecules. The Bragg pattern from the fiber containing these triple-stranded polynucleotide molecules corresponds to a trigonal cell with a = b = 2.71 nm c = 3.65 nm. The molecules are 12, helices.

Tn orcTer to extend these conformational energy studies to the analysis of multi-stranded nucleic acid systems, it is necessary to devise a procedure to identify the arrangements of the polynucleotide backbone that can acconmodate double, triple, and higher order helix formation. As a first step to this end, a computational scheme is offered here to identify the double helical structures compatible with given base pairing schemes. 

Only two kinds of modification of the classical Crick-Watson polynucleotide structure (Figures 10.38 and 10.39) have to this point been considered. These are (1) the occurrence of minor or unusual bases in natural samples of DNA and RNA, and (2) the oecurrence of alternative inter-base H bonding schemes in synthetic oligonucleotides. The latter can be associated with mismatched and no-matched base pairs, or the formation of triple, quadruple or other helical arrangements. 

Anti-poly G poly C antibodies have been demonstrated by immunodiffusion and by complement fixation in the sera of rabbits immunized with poly G-poly C — MBSA (Michelson et al., 1971 Nahon-Merlin et al., 1971). The anti-poly G poly C antibodies react not only with poly G poly C but also with a large number of double-helical complexes such as poly A poly U, poly I poly C and poly dG poly dC. It is nevertheless to be noted that the complex poly A poly I in which two purine polynucleotides are involved is not precipitated by these antibodies, which is readily explained by the special stereochemical structure of this complex. The anti-poly G poly C antisera nevertheless precipitate poly iso A poly I, but in this case it can be considered that displacement of the glycosyl-hnkage from N to in polyisoadenylic acid converts this polynucleotide into an analogue of poly C. The complex is thus effectively between a poly purine ribonucleotide and a poly pyrimidine ribonucleotide as in the case of other complexes such as poly A poly U and poly I poly C. Immune sera against poly G poly C also react with the triple-stranded complex 2 poly G poly C. In addition they can precipitate one or the other of the component polynucleotides of the homologous complex. 

Abbreviations DNA deoxyribonucleic acid RNA ribonucleic acid rRNA ribosomal RNA tRNA transfer RNA. A adenine U uracil G guanine C cytosine, poly A polyadenylic acid poly U polyuridylic acid poly C polycytidylic acid poly I poly-inosinic acid poly G polyguanylic acid. The letters r and d refer to the ribose or deoxy-ribose series. Complexes between the polynucleotides are written as follows polyG poly C double-stranded helical complex of poly G and poly C 2 poly G poly C, triple-stranded complex. BSA bovine serum albumin MBSA methylated bovine serum albumin. N nitrogen. AMV Avian myeloblastosis virus NDV Newcastle disease virus. SLE systemic lupus erythematosus. 

Another y9-(1 3)-D-glucan, named schizophyllan as an antitumor polysaccharide, has been obtained from Schizophylium commune [8,9]. Schizophyllan has similar chemical structure and triple-helix as lentinan [17], as shown in Figure 4. Since Sakurai and Shinkai were the first to find that schizophyllan may form a helical complex with single-stranded homo-polynucleotides [18], many works about preparing a complex of schizophyllan and... 

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