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

Abstract

The amino acid sequence of a novel G protein α subunit (G xα) 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 ( M r 40 519) which is closely related to G iα proteins. The amino acid sequence homology between G xα and human myeloid G iα is 86% with 15 nonconservative substitutions. G xα also shares 86% homology with both rat brain and mouse macrophage G iα but is more homologous (94%) to bovine brain G iα with only 5 nonconservative amino acid differences. G proteins previously termed G iα may fall into at least two distinct groups, with one including human myeloid G iα, rat brain G iα and mouse macrophage G iα; and other G xα; and bovine brain G iα. One group probably contains true G i and the other a new class of G protein whose function remains to be determined.