Investigations into the structure and mechanisms regulating the expression of the genes involved in catecholamine biosynthesis have led to the isolation of a cDNA coding for bovine adrenal tyrosine hydroxylase (TH). The 1,722 bp cDNA contains the complete coding sequence and 3' untranslated region of the TH mRNA. The nucleotide sequence of the cDNA and the deduced amino acid sequence were compared to those reported for rat and human TH. Bovine TH shares 85% and 84% amino acid sequence identity with that of rat and human TH, respectively. Alignment of the amino acid sequences of rat, bovine, and human TH reveals that 79% of the residues are identical in all three species, indicating a strong evolutionary conservation of enzyme structure. Moreover, three of the four putative phosphorylation sites located in the N-terminal region of TH are conserved in these animal species. There are, however, some interspecies differences in TH gene products. The 3' untranslated region of bovine TH mRNA is 56 and 97 nucleotides shorter than rat and human TH mRNA, respectively. Additionally, the bovine protein is 7 and 6 amino acids smaller than its rat and human homologues. All of the absent amino acid residues of bovine TH are missing from an alanine-rich region in the N-terminal portion of the rat and human proteins (amino acids 51-68). Comparison of the size of bovine and rat TH mRNA and protein by northern blot and immunoblot analyses yielded differences consistent with those predicted from the nucleotide sequence data.