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 Gs, Gi, and Go, sequences have not been reported for the γsubunits 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 Gs, Gi, and Go 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 Mr of 7850. The amino acid sequence predicted for the adrenal cDNA clone was identical to that determined for one form of the y 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 cDN A 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 Gs, Gi, and Go in brain.