Figure 3

Induction of IFN-α/β by Y-form DNA is independent of the G quadruplex. (a) G-quadruplex assembly: four guanosines form a planar structure, mediated by hydrogen bonds and stabilized by a central cation (gray). R, deoxyribose backbone. (b) Structures and sequences of YSD or short blunt DNA used in c–e. (c) Native PAGE of G_n-YSD variants (numbers above lanes correspond to models in b). (d) Circular-dichroism melting curve at 295 nm, with the ellipticity of YSD variants or blunt-end DNA (numbers in parentheses and diagrams at left match those in b) measured at 30–70 °C. (e) ELISA of IFN-α in supernatants of chloroquine-treated human PBMCs 20 h after transfection of G_n-YSD variants (numbers and diagrams below plots match those in b); results are presented relative to those of cells transfected with G₃-YSD variant 3 (left) or variant 5 (right), set as 100%. (f) ELISA of IFN-α (bottom) as in e, after transfection of 26-nucleotide G₂-YSD with stepwise substitution of terminal guanosines (G) with deazaguanosine (Z; left) or inosine (i; right); top, chemical structure of 2′-deoxy-7-deazaguanosine and 2′-deoxy-inosine. Numbers adjacent to stems (b,d–f) indicate stem length (sequences of DNA structures, Supplementary Table 1). Data are representative of two experiments (c,d) or are pooled from two (e, f, right) or three (f, right) experiments with one or two biological replicates in each (e,f; mean and s.e.m. of n = 3 donors (e), n = 6 donors (f, left) or n = 4 donors (f, right)).