Polynucleotides, synthetic, double-helical complexes

The anti-poly I poly C antibodies react not only with RNA of reovirus but also, though to a lesser degree, with RNA extracted from mammalian cells (Fig. 4). Comparison of the efficiency of inhibition of the cross-reaction with mammahan RNA by RNA of reovirus, by double-helical complexes of synthetic polynucleotides and by single-stranded polynucleotides, has shown that the antibodies anti-poly I poly C react especially with double-stranded conformational determinants of the RNA. None of the single-stranded polynucleotides is capable of totally inhibiting the reaction with RNA whatever... 

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. 

It is essentially the cross-reactions with another double-helical complex, poly A poly U, which have been studied with immune sera of mice and hamsters. These cross-reactions have been observed very frequently with immune sera of RAP mice and B/W mice and to a lesser degree with the sera of hamsters poly A poly U is the best inhibitor of the reaction between anti-poly I poly C of mice and the homologous antigen (Lacour et al., 1971 Steinberg et al., 1971). The role of the bases in this immunoreaction does not appear to be essential. It is probable that, as in rabbit, these antibodies recognize double-helical structures. While there is similarity in the reactions of the sera of the three species with synthetic polynucleotide double-helical complexes, the cross-reactions of the anti-poly I poly C antibodies with nucleic acids are very different in the rabbit, the mouse, and the hamster (Table 4). 

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