SRP-dependent membrane integration of the beta-subunit of Na+,K+-ATPase.

cDNA clones coding for either full-length or truncated forms of the beta-subunit of the Na+,K+-ATPase from pig kidney were engineered into a transcription vector based on a T7 promotor. In vitro transcription and subsequent translation of the mRNA in the presence of rough microsomes (RM) yielded beta-subunit molecules that were N-glycosylated and correctly inserted into the membrane. The signal peptide was not cleaved off. This membrane integration was found to be dependent on the function of the signal recognition particle (SRP). Several lines of evidence suggest that the hydrophilic aminoterminal domain of 34 amino acid residues preceding the postulated signal sequence is located on the cytoplasmic side whereas the carboxyterminal glycosylated domain is located on the exoplasmic side of the ER (endoplasmic reticulum)-membrane (type II membrane protein).