FIG. 1.

Constructs of chimeric and mutant NA TMDs. Portions of the TR and NA TMDs were swapped to construct four chimeric TMDs (construct no. 5 to 8), as described in Materials and Methods. For the mutants (construct no. 9 to 15), sets of 4 or 5 amino acids in the NA TMD were replaced by alanines. The six amino acids at the NH₂ terminus of TRΔ57 and the other constructs consist of the first two residues (MM) plus the last four residues (KPKR) of the TR cytoplasmic tail. □, amino acid from NA sequence; ○, amino acid from the TR sequence. The lowercase letters represent amino acids neither from the NA sequence nor from the TR sequence but introduced or replaced due to creation of restriction enzyme sites. The numbers at the top represent amino acid positions with respect to the NA sequence.