Cloning of quail tyrosine hydroxylase: amino acid homology with other hydroxylases discloses functional domains.

A cDNA clone containing the entire coding region of quail tyrosine hydroxylase (TH) has been isolated and analyzed. Comparison with rat and human THs and phenylalanine hydroxylases reveals several highly conserved domains. Two of them, shared by all these hydroxylases, are localized in the central and C-terminal parts of the molecules, and most probably include the active site. Two others are found only in the TH molecules. One contains putative sites of phosphorylation and is implicated in the posttranslational regulation of the enzyme. The second highly preserved domain, consisting of a stretch of 21 amino acids, is presumably associated with an important feature of the enzyme that remains to be identified.