a, We assessed whether self-assembly of the dipeptidase mutant takes place at low concentrations. We made serial dilutions of the dipeptidase fused to YFP and then induced self-assembly by addition of 10× PBS to reach a final concentration of 1× PBS (137 mM NaCl, 2.7 mM KCl, 10 mM Na2HPO4, 1.8 mM KH2PO4, pH 7.4). We then incubated the samples for 2 h at 30 °C, spun them down, and pipetted 10 μl of the supernatant to analyse its protein concentration by fluorescence microscopy. b, The concentration of protein in the supernatant relative to the original concentration gave us the fraction of soluble protein. c, The fraction of soluble protein was situated between 0.04 and 0.25 at all concentrations studied, indicating that self-assembly does occur at concentrations as low as 9 nM and probably lower. Error bars span two standard errors and were calculated on the basis of four replicates.