Identification of the GTP-binding protein encoded by Gi3 complementary DNA

Three closely related, but distinct, GTP-binding proteins (G-proteins) are encoded by cDNAs arbitrarily designated Gi1, Gi2, and Gi3. The in vitro translated products of mRNAs prepared from Gi1, Gi2, and Gi3 cDNAs migrate as 41-, 40-, and 41-kDa proteins, respectively, on sodium dodecyl sulfate-polyacrylamide gels. Antisera were raised against synthetic decapeptides corresponding to a divergent sequence (residues 159-168 for Gi1 and Gi3; 160-169 for Gi2) of the three cDNAs and tested on immunoblots for reactivity with three purified G-proteins, G41 and G40 from brain and G41 from HL-60 cells. LD antisera (Gi1 peptide) react only with brain G41. LE antisera (Gi2 peptide) react only with brain G40, and SQ antisera (Gi3 peptide) react exclusively with HL-60 G41. The results indicate that the 41-kDa G-protein purified from HL-60 cells differs from the purified brain 41-kDa protein and suggest that the HL-60 cell protein corresponds to that encoded by Gi3 cDNA.