J. Biol. Chem., Vol. 259, Issue 22, 14217-14221, Nov, 1984
Site of synthesis of the alpha and beta subunits of the Na,K-ATPase in brine shrimp nauplii
JA Fisher, LA Baxter-Lowe and LE Hokin
Developing nauplii (embryos) of the brine shrimp Artemia salina are an
excellent model system for studying the biogenesis of the sodium- and
potassium-activated adenosine triphosphatase (Na,K-ATPase). The nauplii
exhibit a burst of Na,K-ATPase synthesis between 6 and 32 h of development
(Peterson, G. L., Churchill, L., Fisher, J. A., and Hokin, L. E. (1982) J.
Exp. Zool. 221, 295-308). We have now determined the sites of synthesis of
the alpha and beta subunits of the Na,K-ATPase in developing A. salina
nauplii. Membrane-bound and free polysomes were isolated from nauplii, and
RNA was extracted from the polysomes. The polysomal RNA was translated in
vitro in a rabbit reticulocyte lysate, and the translation products were
immunoprecipitated by anti-subunit antisera. The immunoprecipitated
proteins were resolved by sodium dodecyl sulfate-polyacrylamide gel
electrophoresis and visualized by fluorography. Our data show that the
alpha subunit precursor is synthesized on membrane-bound polysomes and the
beta subunit precursor is synthesized on free polysomes. In addition, the
alpha subunit precursor appears as two separate peptides on sodium dodecyl
sulfate- polyacrylamide gels, which suggests that the two alpha subunit
forms seen in mature brine shrimp Na,K-ATPase are products of two distinct
messenger RNAs. The beta subunit precursor appears as a single discrete
band, unlike the mature beta subunit, which appears as a diffuse band.