A novel GTP binding protein (G protein) alpha subunit cDNA was isolated from a T cell leukemia cell line, Jurkat, utilizing polymerase chain reaction (PCR). The predicted amino acid sequence of this G protein alpha subunit showed the highest identity (96.6%) to bovine cone cell-specific transducin (Tc alpha). The organization of the coding region of this G protein alpha subunit gene was composed of 8 exons and 7 introns. Northern hybridization revealed the presence of this G protein message in a retinoblastoma cell line, Y79. In Jurkat, however, the message was detectable only by reverse transcription/PCR. Taken together, this novel G protein alpha subunit must be human Tc.