FIG. 3.

(A) ¹³¹I-labeled Ad2 knob mutants (C428N and SP/EA) and unlabeled wild-type (WT) Ad2 knob protein were incubated for 5 min at room temperature in buffer alone (lanes 2, 4, and 6, respectively) or in buffer containing the recombinant immunoglobulin variable-type domain of CAR (lanes 3, 5, and 7, respectively) prior to electrophoresis in polyacrylamide gels under nondenaturing conditions to detect the formation of knob-CAR complexes. Samples of CAR D1 alone were loaded in lanes 1 and 8. Proteins were visualized by staining the gel with Coomassie blue. (B) SDS-polyacrylamide gel analysis, as described for Fig. 1, of wild-type and mutant Ad2 knob proteins after labeling with ¹³¹I by the iodobead method. Iodination partially destabilized the C428N (lane 4) but not the SP/EA (lane 2) mutant. Proteins were visualized by staining the gel with Coomassie blue.