Comparison of the UmuC peptide with the Pol II peptide. Only a single amino acid change in observed between the β-binding motifs. The structures are shown in stick representation with atomic colouring, solvent molecules are displayed as spheres. The UmuC complex is shown with the clamp residues and associated solvent molecules in magenta and the peptide in light pink. The Pol II complex is shown with the clamp residues in green and the peptide and solvent molecules in light green. Positions of the binding motif are indicated by arrows where visible in the view. The Gly-781/Asn-359 substitution is highlighted by a dashed circle, indicating the presence of a solvent molecule in the Pol II structure replacing the asparagine side chain from the UmuC peptide. The positions of Arg-152 are identical in the two structures. The N- and C-terminal regions of the peptide are indicated.