Figure 2.

Proteinase K sensitivity of WT and mutant HAs. Cells expressing WT and mutant HAs were metabolically labeled with ³⁵[S]-TransLabel, treated with 8 μg/ml trypsin for 6 min at RT, and then incubated at the indicated pH for 15 min at 37°C, reneutralized, and lysed in an NP-40 cell lysis buffer. Cell lysates were then digested with 0.2 mg/ml proteinase K for 30 min at 37°C. The proteins were immunoprecipitated with the Site A mAb, resolved by SDS-PAGE, and subjected to phosphorimager analysis.