Expression of the avian Na,K-ATPase subunits in Dictyostelium discoideum

This study explored whether Dictyostelium discoideum can be used to express the avian Na,K-ATPase, a heterodimeric membrane protein. Dictyostelium was able to express mRNAs encoding the avian Na, K-ATPase subunits. However, Dictyostelium expressed avian Na, K-ATPase protein when only when a Dictyostelium consensus ribosomal binding sequence, AAAATAAA, was inserted in front of the open reading frames of the alpha1- and beta1-subunit cDNAs and the first eight codons following the start-translation codons were changed to Dictyostelium preferred codons. These modified mRNAs appeared to be much less stable than the forms that were not readily translated. Dictyostelium could express the avian beta-subunit alone but only expressed the alpha1-subunit when the beta1-subunit was co-expressed. Subunit assembly occurred in cells expressing both alpha1- and beta1-subunits. The bulk of the exogenously expressed sodium pump subunits remained in an intracellular compartment, presumed to be the endoplasmic reticulum. Dictyostelium exported little or no Na, K-ATPase or free beta-subunit to the plasma membrane.