(A,B) Structural representations of the phe-tRNA (PDB ID 1EHZ) and P4–P6 subdomain of the L-21 T. thermophila group I intron (PDB ID 1GID) crystal structures, respectively. Base-normal vectors are drawn and colored according to helix affiliation. (C,D) Illustrations of base-normal vectors with RNA structural representation not shown. (E,F) Same as above, but all base-normal helices have been translated to the origin while maintaining the same orientation. The three eigenvectors (λ1, λ2, and λ3) are rendered as red, blue, and green vectors with spherical tips, respectively. In all three representations the same frame of reference is maintained. This article reports on the statistical tests of the coplanar and bipolar nature of RNA base-normal vectors.