Triple-stranded complexes

In each section double stranded complexes are shown first, followed by triple stranded complexes. Strands 1 and 2 are considered to be Watson-Crick hydrogenbonded and thus anti-parallel, except otherwise indicated. In the triple-strand case the Hoogsteen bound strand is strand 3 and thus parallel to strand 1. In the homopolymer complexes the strands are generally parallel. 

In the following Table 3 both double and triple stranded complexes are listed. If the stoichiometry poly(A) poly(U)=l l then three 7 , values shall be observed depending on ionic strength below 0.15 M Na, and 7 2-3 nd Tm3-1 above this ionic strength. Conversely, if the poly(A) poly( stoichiometry... 

Poly(l) forms a triple-stranded complex with poly(A). 

In contrast, immunochemical techniques which have already shown a sensitivity sufficient to distinguish single from double-stranded complexes and two-stranded hehces from triple-stranded complexes may be extremely useful in such studies. Indeed, recent work using spontaneous antibodies such as those found in systemic lupus erythematosus (SLE) sera, as well as experimentally induced antibodies, has demonstrated immunochemical differences between different double-stranded hehcal complexes and it is clear that development of this approach will be extremely fruitful. 

In order to elucidate the role of conformation of the immunogen, animals were immunized with complexes of polyribonucleotides (double- or triple-stranded) associated with MBS A. The antibodies obtained reacted specifically with double- or triple-stranded complexes and it was concluded that the specificity was determined by the macromolecular conformation of the immunogen (Nahon et al., 1967 Lacour et al., 1968 Michelson et al., 1971). Immunization of rabbits with DNA-MBSA or with double-stranded polynucleotide complexes adsorbed to MBS A ehcits antibodies belonging to the macroglobulin class (Stollar and Sandberg, 1966 Nahon-Merlin et al., 1973). 

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. 

Antibodies with a strict specificity for triple-stranded structures do not react with either RNA or DNA. Since the bases are not readily accessible in a triple-stranded complex it is possible that the polyribose phosphate... 

The existence of conformational determinants has been clearly demonstrated through the use of synthetic polynucleotides in double-hehcal structures and in triple-stranded complexes. It has also been shown that the specificity of antibodies is determined by the macromolecular conformation of the immunogen. Thus single-stranded polynucleotides induce formation of antibodies specific for the single-strand, while double-stranded hehcal complexes of polynucleotides induce antibodies specific for these structures, and antibodies specific for triple-strand structures are induced by the triple-stranded polynucleotide complexes. 

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. 

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