Identification of a novel gamma-subunit from bovine brain GTP binding regulatory proteins (Gi/o)

Heterogeneity of the gamma-subunit of G proteins has been demonstrated by cDNA cloning and by partial sequence analyses. We have isolated two intact beta gamma-subunit isoforms from bovine brain Gi/o mixture, in which only gamma subunits are distinct (Sohma, H., et al. (1992) Biochem. Biophys. Res. Commun. 184, 175-182). In this study, we isolated the gamma-subunit isoforms, gamma-I and gamma-II, and examined their amino acid sequences. Both gamma-I and gamma-II had blocked N-terminal amino acid residues, and the terminal amino acids of both were able to be truncated by an acylamino-acid-releasing enzyme. Gamma-I seemed to be identical with the gamma-subunit reported elsewhere, while the gamma-II appeared to be a novel protein. Antibodies to synthetic peptides based on the part of the amino acid sequences of gamma-I and gamma-II reacted specifically to gamma-I and gamma-II, respectively.