(A) Illustration of the statistical test for coplanarity or bipolarity in the distribution of base-normal vectors for all known RNAs. The expected average angular dispersion (θ[n]) is plotted as a black line (for randomly generated vector orientations) while the two dotted lines indicate 95% confidence intervals. The measured average angular dispersion for each RNA is plotted as a cross (red, green, cyan, and blue are tRNAs, rRNAs, catalytic RNAs, and uncategorized RNAs, respectively). Three hundred thirty out of 331 (99.9%) of the crosses fall below the 95% confidence interval. (B) Same as in A, but the distribution of aggregate helical mean-axis vectors are being tested. Sixty-two percent (208/331) of the RNA structures exhibit statistically significant global coaxial arrangements of helices.
