Fig. 3. Protein crosslinking experiment. Proteins in ARL cells were crosslinked with DTBP and resolved, without prior reduction of disulfide bonds by SDS-PAGE (1D). The sample-lane was excised, incubated with DTT to cleave DTBP and subjected to the second dimension SDS-PAGE (2D). Blotted proteins were stained with Coomassie Brilliant Blue (A), destained and probed with McAb 351 (B) and finally reprobed with an anti-vimentin antibody (C). Non-crosslinked proteins form a curved diagonal in 2D (A); S1 proteins C2 and D2 (B) and vimentin (C) are seen on horizontal lines at the monomer sizes: they were crosslinked to the products of various sizes. Their non-crosslinked forms are seen on the left as strongly stained spots.