Human Gi protein α‐subunit: deduction of amino acid structure from a cloned cDNA

Abstract
The amino acid sequence of the α‐subunit of Gi, the human adenylate cyclase inhibiting GTP‐binding protein, has been deduced from the nucleotide sequence of a DNA clone complementary to G, mRNA from differentiated U937 cells. The cDNA encodes a polypeptide of 355 amino acids (M r 40456). The amino acid sequence homology between human G and rat, murine, and bovine G 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 G mRNA as well as a 3.6‐fold increase in the 41 kDa pertussis toxin substrate presumed to be G. Thus, increased levels of this G‐protein are associated with monocyte differentiation and appear to be regulated transcriptionally.