Figure 4.

DSP crosslinking of cells expressing tailless A2 reveals an association between US11 or US2 and tailless A2. Cells exposed to the crosslinker DSP (see Materials and Methods) were lysed in Nonidet P-40 buffer. Folded MHC class I products were recovered by immunoprecipitation with the W6/32 antibody. A portion of this immunoprecipitate was loaded directly (first IP). The remainder was denatured in SDS without reductant and reprecipitated with αHC and either α-US2 or α-US11 antibodies. Reimmunoprecipitation with α-US11 antibody recovers tailless A2, indicative of an association between them (a, right lane). Likewise, US2 antibodies recover crosslinked tailless A2 (b, right lane). Reduction of the thiol-cleavable crosslinker before SDS/PAGE analysis dissociates the crosslinked molecules and yields the constituent polypeptides that then migrate at their characteristic molecular weights.