The 35- and 36-kDa β Subunits of GTP-binding Regulatory Proteins Are Products of Separate Genes
The wide range of functions attributed to GTP-binding regulatory proteins (G proteins) is reflected in the structural diversity which exists among the α, β, and y subunits of G proteins. Recently two cDNA clones encoding β subunits, β_1 and β_2, were isolated from bovine and human cDNA libraries. We report here that the β_2 gene encodes the 35-kilodalton (kDa) component of the β_(35)/β_(36) subunit of G proteins and that the β_1 gene encodes the 36-kilodalton component. The in vitro translation product of the β_2 cDNA co-migrates with the 35-kDa β subunit (β_(35)), while the in vitro product of the β_1 cDNA co-migrates with the 36-kDa β subunit (β_(36)) on denaturing polyacrylamide gels. In addition, antisera generated against synthetic β_2 peptides bind specifically to the β_(35) component of isolated G proteins and to a 35-kDa protein in myeloid cell membranes. Our results suggest that the two β subunits could serve distinct functions, as they are derived from separate genes which have been highly conserved in evolution.