Existence of two γ subunits of the G proteins in brain

Although amino acid sequences have been determined for the α and β subunits of G(s), G(i), and G(o), sequences have not been reported for the γ subunits of these G proteins. In the present paper, we determined the sequences of peptides prepared by partial proteolysis of two different forms of the γ subunit of G(s), G(i), and G(o) from bovine brain. Using oligonucleotide probes based on the sequences of two of these peptides, a cDNA clone was isolated from a bovine adrenal cDNA library. This clone contained a 0.9-kilobase cDNA insert that included an open reading frame of 213 bases encoding a 71-amino acid polypeptide with an estimated M(r) of 7850. The amino acid sequence predicted for the adrenal cDNA clone was identical to that determined for one form of the γ subunit from brain. In addition, an antibody to a peptide based on the predicted amino acid sequence of this cDNA clone reacted specifically with one of the brain γ subunits, indicating the adrenal cDNA clone encodes a γ subunit present in both adrenal gland and brain. Also, evidence is presented, demonstrating the existence of a second, structurally distinct, form of the γ subunit of G(s), G(i), and G(o) in brain.