Genomic Organization of the Murine G Protein (3 Subunit Genes and Related Processed Pseudogenes

The functional significance of heterotrimeric guanine nucleotide binding protein (G protein) for the many physiological processes including the molecular mechanisms of drug addiction have been described. In investigating the changes of mRNA expression after acute psychostimulant administration, we previously identified a cDNA encoding a G protein pi subunit (Gpi) that was increased up to four-fold in certain brain regions after administration of psychostimulants. The mouse Gpi gene (the mouse genetic symbol, GNB1) was mapped to chromosome 4, but little was known of its genetic features. To characterize the GNB1 gene further, we have cloned and analyzed the genomic structures of the mouse GNB1 gene and its homologous sequences. The GNB1 gene spans at least 50 kb, and consists of 12 exons and 11 introns. The exon/intron boundaries were determined and found to follow the GT/AG rule. Exons 3-11 encode the Gpi protein, and the exon 2 is an alternative, resulting in putative two splicing variants. Although intron 11 is additional for GNB1 compared with GNB2 and GNB3, the intron positions within the protein coding region of GNB1, GNB2 and GNB3 are identical, suggesting that GNB1 should have diverged from the ancestral gene family earlier than the genes for GNB2 and GNB3. We also found the 5′-truncated processed pseudogenes with 71-89% similarities to GNB1 mRNA sequence, suggesting that the truncated cDNA copies, which have been reverse-transcribed from a processed mRNA for GNB1, might have been integrated into several new locations in the mouse genome.