Figure 7.

(A) Human PDGFR-β gene promoter. (B) PDGFR-β promoter G-quadruplex forming sequences. (C) (top) PD-5Mid forms a novel broken-strand G-quadruplex. Instead of using four G runs of three or more consecutive guanines, PD-5Mid uses the G₂ run III to form a “broken” G-strand consisting of guanines from different G runs (left). Two equilibrating vG4 (middle), which can be filled-in and stabilized by endogenous guanine metabolites, and the NMR structure of the dGMP complex (right). (bottom) PD-3End forms two equilibrating broken-strand G-quadruplexes. The G₂ run VII moves up or down within the G-core to accommodate an inserted guanine from the 3′ or 5′ nonadjacent flanking regions into the external tetrad.