Comparison of cDNA sequences from multiple sources predicts a genus of highly homologous but structurally distinct G protein α-subunits, designated as Giα, that may include the α-subunit of the functionally defined adenylate cyclase inhibitory G protein. Using specific oligonucleotide probes on Northern blots, we show that Giα−2 and Giα−3, but not Giα−1, are expressed in HL60 cells. Antisera raised against synthetic peptides from regions predicted to be conserved (AS6) and divergent (LE3) among Giα subtypes bind to a 40 kDa protein in Western blots of HL60 membranes. AS6 identifies an additional protein at 41 kDa. Thus, Northern blot and immunoblot results show that at least two Giα subtypes, a 40 kDa protein likely to correspond to Giα−2 and a 41 kDa protein possibly representing Giα−3, may be expressed in a single cell type.
