Corn, a 28-nucleotide RNA, increases yellow fluorescence of its cognate ligand 3,5-difluoro-4-hydroxybenzylidene-imidazolinone-2-oxime (DFHO) by >400-fold. Corn was selected in vitro to overcome limitations of other fluorogenic RNAs, particularly rapid photobleaching. We now report the Corn–DFHO co-crystal structure, discovering that the functional species is a quasisymmetric homodimer. Unusually, the dimer interface, in which six unpaired adenosines break overall two-fold symmetry, lacks any intermolecular base pairs. The homodimer encapsulates one DFHO at its interprotomer interface, sandwiching it with a G-quadruplex from each protomer. Corn and the green-fluorescent Spinach RNA are structurally unrelated. Their convergent use of G-quadruplexes underscores the usefulness of this motif for RNA-induced small-molecule fluorescence. The asymmetric dimer interface of Corn could provide a basis for the development of mutants that only fluoresce as heterodimers. Such variants would be analogous to Split GFP, and may be useful for analyzing RNA co-expression or association, or for designing self-assembling RNA nanostructures.

Corn 是一种 28 核苷酸 RNA，可将其同源配体 3,5-二氟-4-羟基苯亚甲基-咪唑啉酮-2-肟 (DFHO) 的黄色荧光增强超过 400 倍。在体外选择玉米是为了克服其他荧光 RNA 的局限性，特别是快速光漂白。我们现在报道了 Corn-DFHO 共晶结构，发现功能物种是准对称同二聚体。不同寻常的是，二聚体界面缺乏任何分子间碱基对，其中六个未配对的腺苷打破了整体的双重对称性。同型二聚体在其原聚体间界面处封装了一个 DFHO，将其与来自每个原聚体的 G-四联体夹在中间。玉米和绿色荧光菠菜 RNA 在结构上无关。他们对 G-四链体的集中使用强调了该基序对于 RNA 诱导的小分子荧光的有用性。玉米的不对称二聚体界面可以为仅以异二聚体形式发出荧光的突变体的开发提供基础。此类变体类似于 Split GFP，可用于分析 RNA 共表达或关联，或用于设计自组装 RNA 纳米结构。