Characterization of SARS-CoV nsp10 in complex with nsp16. (a) Gel-filtration chromatogram of the SARS-CoV nsp10–nsp16 complex. The nsp10–nsp16 complex eluted from the Strep-Tactin column was analyzed on a 16/60 S200 gel-filtration column and the elution of protein and nucleic acid was followed by measuring the absorption at 280 nm (blue) and 260 nm (orange), respectively. The main peak eluting after 90 ml corresponds to elution of a 50 kDa protein. (b) Cross-linking experiment. The purified SARS-CoV nsp10–nsp16 complex was loaded onto a 4–12% NuPAGE gel and stained using Coomassie Blue. Lane MK, molecular-weight markers; lane 1, 4 µg non-cross-linked nsp10–nsp16 complex, lane 2, 4 µg of the nsp10–nsp16 complex incubated overnight at 277 K with 0.005% SAB cross-linker.