A genomic clone spanning the mouse rod transducin alpha subunit (Tr alpha) gene has been isolated by screening a mouse genomic library with a bovine Tr alpha cDNA clone. The coding region of the mouse Tr alpha gene reveals an 88.7% nucleotide identify and 99.7% amino acid identity with bovine Tr alpha. The mouse Tr alpha gene is composed of 8 exons and 7 introns within its coding region. These introns are in the same locations as introns in human Gi alpha genes, that encode G proteins closely related to transducin. Primer extension, RNA sequencing, and S1 nuclease protection analyses indicate that the mouse Tr alpha gene transcription start site is 84 bases upstream of the initiation codon. Northern blot analysis shows that the mouse Tr alpha is expressed in the retina, but not in brain, kidney, liver, or heart.