cDNAs encoding the baboon thrombin receptor indicate a primate transcription start site upstream of putative sites reported for the human gene.
Two cDNAs encoding the thrombin receptor of baboon vascular smooth muscle cells have 5'-untranslated regions that begin upstream of multiple putative transcription initiation sites reported for the closely related human receptor gene. The extent of these baboon 5'-untranslated cDNA regions and their close similarity to the corresponding human sequences suggest that there is only one transcription initiation site of the primate thrombin receptor gene, which might be linked to a typical TATA-box previously identified in the upstream region of the human gene. It is possible that all primates have a unique thrombin receptor gene transcription start site. Inferences drawn from the baboon system may be usefully extrapolated to the human, in view of the extensive similarities seen between the nucleotide sequences of baboon and human thrombin receptor gene sequences in the 5'- untranslated and coding regions. The extents of the 5'-untranslated region of the baboon cDNAs argue that the "multiple" transcription start sites identified for the human gene are artifactual. The striking differences in the reported baboon and human transcription start sites warrant further investigation in view of the significant role played by the thrombin receptor in numerous vascular and cellular growth responses.