The carboxyl-terminal 161 amino acids of the Na,K-ATPase α-subunit are sufficient for assembly with the β-subunit

Chimeric cDNAs encoding regions of the Na,K-ATPase α-subunit and a sarcoplasmic reticulum Ca²⁺-ATPase were constructed and expressed together with the avian Na,K-ATPase β-subunit cDNA in COS-1 cells to determine which regions of the α-subunit are required for assembly with the β-subunit. Assembly was assayed by immune precipitation of the chimeric subunit with a monoclonal antibody to the avian β-subunit. A chimera composed of the amino- terminal two-thirds of the Na,K-ATPase and carboxyl-terminal one-third of the Ca²⁺-ATPase did not assemble with the avian β-subunit. In contrast, the reciprocal chimera, containing the carboxyl-terminal one-third of the Na,K- ATPase, assembled with the β-subunit. A third chimera, in which 161 amino acids of the Na,K-ATPase carboxyl terminus replaced the corresponding amino acids of the Ca²⁺-ATPase carboxyl terminus, also assembled with the β- subunit. These results suggest that the aminoacyl residues of the Na,K-ATPase α-subunit critical for subunit assembly lie within the carboxyl-terminal 16% of the sequence.