THE HUMAN TRYPTOPHAN-HYDROXYLASE GENE - AN UNUSUAL SPLICING COMPLEXITY IN THE 5'-UNTRANSLATED REGION

We report the isolation and the organization of the gene encoding huma n tryptophan hydroxylase (TPH) and an analysis of the corresponding mR NAs. The gene spans a region of 29 kilobases, which contains at least 11 exons and a variably spliced 5'-untranslated region (5'-UTR). The s equence of the coding region and the majority of the positions of the intron-exon boundaries of human TPH gene are very similar to those enc oding human tyrosine hydroxylase and phenylalanine hydroxylase, the ot her members of the aromatic amino acid hydroxylase family. Phylogeneti c analysis evidences the early divergence and the independent evolutio n of the three hydroxylase types. TPR cDNA cloning and anchored polyme rase chain reaction revealed a diversity of the TPH mRNA, which is res tricted to the 5'-UTR. Four TPH mRNA species were detected by Northern blot with pineal gland and carcinoid tumor RNAs. These messengers are transcribed from a single transcriptional initiation site, and their diversity results from differential splicing of three intron-like regi ons and of three exons located in the 5'-UTR Analysis by S1 nuclease p rotection revealed that the intron-like regions in the 5'-UTR are most ly unspliced and that TPH mRNA species where the three intron-like reg ions are eliminated are present at low level in pineal gland and not d etectable in carcinoid tumors.