Interactions at the monomer-monomer interface. A. Superposition of known PCNA structures, showing variation in the extent of the monomer-monomer interface. Red – H. volcanii; green – A. fulgidus [PDB:1RWZ]; cyan – P. furiosus [PDB:1GE8]; purple – human [PDB:1VYM] and gold – yeast [PDB:1PLQ]. B. The monomers are coloured separately in red and purple, with individual side chains directly involved in interactions shown in stick representation. Residues at the end of the two β-strands involved are labelled. Hydrogen bonds are indicated by dashed lines. C. Size exclusion profiles of Hv PCNA in 0.2 M KCl (solid line) and 3.0 M KCl (dotted line). The x axis indicates elution volume (mls) and the y axis shows absorbance at 280 nm.