Polynucleotide helix geometry and stability. Spectroscopic, antigenic and interferon-inducing properties of deoxyribose-, ribose-, or 2'-deoxy-2'-fluororibose-containing duplexes of poly(inosinic acid) . poly(cytidylic acid).

Circular dichroism, absorbance temperature profiles, antigenic properties, and interferon-inducing capacity of the nine double-stranded complexes between poly(inosinic acid) and poly(cytidylic acid) [(rI)n . (rC)n] and their deoxy- and 2'-deoxy-2'-fluoro-analogues were studied. The complexes containing only ribose or 2'-fluororibose chains showed similar CD spectra and thermal stabilities. Anti-(rI)n . (rC)n antibodies were well recognized by the duplexes containing 2'-fluororibose in either one strand. These two duplexes were also efficient interferon inducers. Presence of fluororibose in both strands decreased the affinity of anti-(rI)n . (rC)n antibodies slightly and abolished interferon-inducing activity. All polydeoxyriboside-containing complexes showed CD spectra significantly different from the previous group; they showed also 40- to 100-times lower affinity for the anti-(rI)n . (rC)n antibodies, and did not induce interferon. It is concluded that the structure of (rI)n . (rC)n, an A-type helix, is little perturbed by substitution of one or both strands by 2'-fluororibose. Substitution by deoxyribose in either strand considerably changes the structure of the helices. The hybrids containing poly(deoxycytidylic acid) retain at least some of the structural features of the B-type helix poly(deoxyinosinic acid) . poly(deoxycytidylic acid).