MOLECULAR-CLONING AND SEQUENCE DETERMINATION OF CDNAS FOR ALPHA-SUBUNITS OF THE GUANINE NUCLEOTIDE-BINDING PROTEINS-GS, PROTEINS-GI, AND PROTEINS-GO FROM RAT-BRAIN

We have cloned cDNAs encoding .alpha. subunits of the guanine nucleotide-binding proteins Gs, Gi, and Go and determined their nucleotide seqences. Purified preparations of Gi and Go .alpha. subunits (Gi.alpha. and Go.alpha.) from rat brain were completely digested with trypsin, and peptides were subjected to amino acid sequence analysis. By screening of a cDNA library from rat C6 glioma cells with a synthetic probe corresponding to a 17 amino acid sequence, a clone encoding the sequence of Go.alpha. was obtained. Then, the library was rescreened with a Go.alpha. cDNA probe to isolate several strongly or weakly hybridizing clones. cDNAs encoding the complete sequences to Gi.alpha. and Gs.alpha. were thus obtained. From nucleotide sequence analysis, the amino acid sequences of Gs.alpha. and Gi.alpha. were deduced; they contain 394 and 355 amino acid residues (including the initiator methionine), respectively. The calculated molecular weights for Gs.alpha. and Gi.alpha. were 45,663 and 40,499, respectively. The Go.alpha. clone encoded a sequence of 310 amino acid residues that lacked the NH2 terminus. The homology of the .alpha. subunits of Gs, Gi, Go, transducin, and ras-encoded protein is discussed.