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The 35- and 36-kDa beta subunits of GTP-binding regulatory proteins are products of separate genes.

1988; Elsevier BV; Volume: 263; Issue: 11 Linguagem: Inglês

10.1016/s0021-9258(18)60667-2

1083-351X

Thomas Amatruda, Narasimha Gautam, Henry Fong, John K. Northup, M I Simon,

Cellular transport and secretion

The wide range of functions attributed to GTP-binding regulatory proteins (G proteins) is reflected in the structural diversity which exists among the a, B, and y subunits of G proteins.Recently two cDNA clones encoding 0 subunits, B1 and &, were isolated from bovine and human cDNA libraries.We report here that the B2 gene encodes the 35-kilodalton (kDa) component of the @sa/@sa subunit of G proteins and that the B1 gene encodes the 36-kilodalton component.The in vitro translation product of the & cDNA co-migrates with the 35-kDa 6 subunit 0 , while the in vitro product of the cDNA co-migrates with the 36-kDa fi subunit GBsa) on denaturing polyacrylamide gels.In addition, antisera generated against synthetic flz peptides bind specifically to the f l S 8 component of isolated G proteins and to a 36-kDa protein in myeloid cell membranes.Our results suggest that the two B subunits could serve distinct functions, as they are derived from separate genes which have been highly conserved in evolution.G proteins are heterotrimeric proteins which bind guanine nucleotides, possess an endogenous GTPase' activity, and function as intermediaries in transmembrane signaling pathways (1).A general model for G protein action, extrapolated from the mechanism of activation of adenylate cyclase and the mechanism of photoreceptor function, has been proposed.It is suggested that binding of ligand to a transmembrane receptor (or activation by light) induces the a subunit of the G protein to bind GTP.The a subunit with bound GTP then dissociates from the / 3 and y subunits and activates an intracellular effector molecule (1, 2).In this model, the / 3 and y subunits remain associated in a complex which anchors the a subunit in proximity to a transmembrane receptor and se-