Fig. 2. Comparison of cross-linked products to procollagen chains that form either monomers or trimers. Transcripts encoding proα1(III)Δ1, proα1(III)Δ1Cys-Ser, proα2(I)Δ1 and proα2(I):(III)BGR were translated in rabbit reticulocyte lysate in the presence of SP cells. Products of translation were isolated and chemically cross-linked using DSP. Cross-linked samples were immunoprecipitated using the indicated antibodies and separated by SDS–PAGE under reducing conditions. The (A) proα1(III)Δ1, (B) proα1(III)Δ1Cys-Ser, (C) proα2(I)Δ1 and (D) proα2(I):(III)BGR translation products were cross-linked with DSP and separated by SDS–PAGE either before (lane 1) or after immunoprecipitation with antibodies to PDI (lane 2), Hsp47 (lane 3), the α-subunit of P4H (lane 4) or control antibody 9E-10 (lane 5).