Polyribonucleotides, double-stranded complexes

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). 

Differences in the capacity of inhibition by polynucleotides not involved in complementary hydrogen bonds and by double-helical complexes of synthetic polyribonucleotides, or double-stranded viral RNA allow the conclusion that it is above all the regions of associated base pairs which are recognized in the RNA by anti-poly I poly C antibodies. Such complementary double-stranded helical regions have been described especially in tRNA but they have also been shown to exist in ribosomal RNA. These two kinds of RNA were therefore isolated and studied separately. Although both fractions precipitate anti-poly I poly C antibodies, their reactivity is nevertheless very different and rRNA precipitates eight times as much antibody as tRNA. Since tRNA possesses an important tertiary structure, this low reactivity could be explained by the non-accessibility of antigenic sites. 

Thus poly A poly U and poly I poly C induce antibodies specific for the double-stranded structure, and reciprocal cross-reactions between these two polyribonucleotide complexes are constant and quantitatively comparable. A third complex, poly G poly C reacts only feebly with the two preceding immune sera. The h3q)othesis that this immunochemical difference correlates with a stereochemical difference of structure implies that this complex, if it has immunogenic capacity, may induce antibodies with a particular specificity. The validity of this concept has been demonstrated and wiU be discussed next. 

Table 3 (section 3.2.2.2) contains melting temperatures of polyribonucleotide hetero-complexes (including base-modified complexes), both double and triple stranded. 

In order to give DNA immunizing properties Plescia et al. (1964, 1965) complexed the material to MBS A. A certain number of polynucleotides such as denatured DNA, poly dAT, and tRNA associated with MBS A have been used as immunogens by these authors. This method of preparation has been used for other polynucleotides, particularly for single-stranded synthetic polynucleotides and the various double- and triple-hehcal complexes formed from such polyribonucleotides. It appears that secondary structure of these complexes is generally maintained on adsorption onto MBS A, although some of their characteristics could well be modified in this electrostatic interaction. 

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