Human Gi protein alpha-subunit: deduction of amino acid structure from a cloned cDNA.

The amino acid sequence of the alpha-subunit of Gi, the human adenylate cyclase inhibiting GTP-binding protein, has been deduced from the nucleotide sequence of a DNA clone complementary to Gi alpha mRNA from differentiated U937 cells. The cDNA encodes a polypeptide of 355 amino acids (Mr 40456). The amino acid sequence homology between human Gi alpha and rat, murine, and bovine Gi alpha is 98.6, 97.7 and 87.9% respectively. Differentiation of the U937 cells from monoblasts to monocyte-like cells resulted in a 3-fold increase in Gi alpha mRNA as well as a 3.6-fold increase in the 41 kDa pertussis toxin substrate presumed to be Gi alpha. Thus, increased levels of this G-protein are associated with monocyte differentiation and appear to be regulated transcriptionally.