For UV irradiation, we used a 300-W xenon light source (MAX-303 from Asahi Spectra) with a high transmission bandpass filter centered around 310 nm (XAQA310 from Asahi Spectra). We used a light guide (Asahi Spectra) to couple the light into the sample by placing it directly on top of a 0.65-ml reaction tube. Unless otherwise indicated, the brick-like samples were irradiated for 135 min, the pointer samples for 120 min, and the polymerizing brick samples for 30 min. Samples were irradiated in folding buffer (5 mM tris, 1 mM EDTA, and 5 mM NaCl) including 30 mM MgCl2, unless otherwise stated.