DELETION OF NH2-TERMINAL AND COOH-TERMINAL SEQUENCES DESTROYS FUNCTION OF THE OF THE PASE OF RABBIT FAST-TWITCH SKELETAL-MUSCLE SARCOPLASMIC-RETICULUM

Deletion mutants of the Ca2+ ATPase of rabbit fast-twitch skeletal muscle sarcoplasmic reticulum (SERCA1a) were constructed and expressed in COS-1 cells. The mutants were expressed at levels 7- to 15-fold lower than the wild-type and were inactive. In vitro transcription-translation-insertion experiments showed that deletion of transmembrane sequences M(1) and M(2), but not of M(8), M(9), M(10) or the NH2-terminal 30 amino acids inhibited the stable insertion of the enzyme into the membrane. Thus there was no correlation between loss of function and membrane insertion. A signal sequence for membrane insertion may exist in M(1) and M(2).