Figure 3. Pan2 contacts the ribophosphate backbone of poly(A) RNA.

a, Crystal structure of Pan2^UCH-Exo E912A (cartoon, blue) bound to A₇ RNA (sticks, green). Unmodeled loops are represented by dashed lines. Inset: close-up view of the Pan2 exonuclease active site. The electron density represents a feature-enhanced map contoured to 1.3σ. Nucleotides are numbered relative to the scissile bond, which is indicated by an arrow. b, The electron density for the scissile phosphate bond and A₇ substrate are shown in the Pan2 active site. The mesh represents electron density from a feature-enhanced map contoured to 1.8σ. c-d, Protein-RNA interactions between Pan2^UCH-Exo E912A and oligo(A). Putative hydrogen bonds are indicated by dashed lines and interatomic distances are labeled in Ångstroms. e, Surface representation of Pan2^UCH-Exo E912A (blue) bound to A₇ (green). Pan2^UCH-Exo E912A is colored by proximity to A₇ from dark (<3 Å) to light (>7 Å) blue.