The proposed communication relay between the β-clamp pore to the peptide binding site. Gln-149 is proposed to act as a DNA sensor, impacting on the conformation of Asp-150, which in turn substantially interacts with Arg-152, a key clamp residue involved in peptide binding. The co-complex presented has been aligned with the β-clamp/DNA co-crystal structure [PDB:3BEP]. The β-clamps are shown in cartoon form in light blue (UmuC complex) and cyan (DNA complex), with the 148–152 loop shown in stick representation in atomic colouring. The UmuC peptide is shown in magenta, with key hydrogen bonds represented by black dashed lines. DNA is coloured red. The N- and C-terminal regions of the peptide are indicated.