Detection of multiple forms of Gi alpha in HL60 cells

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