Gα_q is the α subunit of one of the heterotrimeric GTP-binding proteins that mediates stimulation of phospholipase Cβ. We report the isolation and characterization of cDNA clones from a frontal cortex cDNA library encoding human Gα_q. The encoded protein is 359 amino acids long and is identical in all but one amino acid residue to mouse Gα_q. Analysis of human genomic DNA reveals an intronless sequence with strong homology to human Gα_q cDNA. In comparison to Gα_q cDNA, this genomic DNA sequence includes several small deletions and insertions that alter the reading frame, multiple single base changes, and a premature termination codon in the open reading frame, hallmarks of a processed pseudogene. Probes derived from human Gα_q cDNA sequence map to both chromosomes 2 and 9 in high-stringency genomic blot analyses of DNA from a panel of human-rodent hybrid cell lines. PCR primers that selectively amplify the pseudogene sequence generate a product only when DNA containing human chromosome 2 is used as the template, indicating that the authentic Gα_q gene (GNAQ) is located on chromosome 9. Regional localization by FISH analysis places GNAQ at 9q21 and the pseudogene at 2q14.3-q21.