Molecular cloning of a new human G protein Evidence for two Giα-like protein families

AbstractThe amino acid sequence of a novel G protein α subunit (Gxα) has been deduced from the nucleotide sequence of a human cDNA clone isolated from a differentiated HL-60 cDNA library. The cDNA encodes a polypeptide of 354 amino acids (Mr 40 519) which is closely related to Giα proteins. The amino acid sequence homology between Gxα and human myeloid Giα is 86% with 15 nonconservative substitutions. Gxα also shares 86% homology with both rat brain and mouse macrophage Giα but is more homologous (94%) to bovine brain Giα with only 5 nonconservative amino acid differences. G proteins previously termed Giα may fall into at least two distinct groups, with one including human myeloid Giα, rat brain Giα and mouse macrophage Giα; and other Gxα; and bovine brain Giα. One group probably contains true Gi and the other a new class of G protein whose function remains to be determined