Genes for two homologous G-protein α subunits map to different human chromosomes

Signal transduction across biological membranes is modulated by a family of related GTP-binding proteins termed G proteins. These G proteins have a heterotrimeric structure composed of α, β, and γ subunits. The α subunits of the G proteins bind GTP and appear to determine the biochemical specificity of the protein. We have recently cloned and characterized cDNA encoding two G-protein α subunits, α(i) and α(h). The former is a substrate for ADP-ribosylation by pertussis toxin. The protein corresponding to α(h) has not yet been identified. These cDNAs encode proteins, which demonstrate 90% sequence identity to one another and also show marked similarity to other G proteins. The present studies were designed to determine whether the genes for these related proteins are clustered on a single human chromosome. Genomic DNA isolated from a panel of mouse-human hybrid cell lines was analyzed by hybridization to cDNAs for α(i) and α(h). Based on the distribution patterns of α(i) and α(h) in cell hybrids, the gene for α(i) was assigned to human chromosome 7, and the gene for α(h) assigned to chromosome 12. These data suggest that the G-protein gene family may be distributed over at least two human chromosomes.