Fig. 5. MHC class I retention mediated by the gp40 chimeric proteins and intramolecular deletion mutants. NIH 3T3 cells were infected with wt-vac and the indicated recombinant vaccinia viruses, respectively. At 5 h post-infection, cells were pulse-labeled for 30 min with [³⁵S]cysteine/methionine. Cell lysates were prepared after the indicated chase periods. MHC class I molecules (H2-L^q) and gp40 derivatives were precipitated with the mAb 28-14-8S (A) and the peptide antiserum against gp40 (B), respectively. Half of the precipitated proteins were digested with endo H. The proteins were separated by SDS–PAGE and visualized by autoradiography. Note that in addition to the endo H-resistant form of the two differently glycosylated protein species corresponding to gp40 and gp37, a slower migrating endo H-resistant protein form is visualized under chase conditions.