Quaternary structure analysis of YqiC. (A) Chemical cross-linking. Cross-linked products were separated via 15% SDS-PAGE followed by Coomassie brilliant blue staining. Protein markers are shown in kilodaltons. The numbers 0, 0.5, 1, and 5 indicate the millimolar concentrations of ethylene glycol bis (succinimidyl succinate) used. (B) Gel filtration coupled to SLS analysis. The protein was run on a Superdex-75 column and eluted with 50 mM Tris-HCl, 150 mM NaCl buffer (pH 8). The molecular mass of the protein was calculated relating its light scattering at 90° (dashed line) and refractive index (solid line) signals, and comparison of this value with that obtained for BSA as a standard.