A NOVEL RAT TYROSINE-HYDROXYLASE MESSENGER-RNA SPECIES GENERATED BY ALTERNATIVE SPLICING

Tyrosine hydroxylase (TH) catalyzes the first and rate-limiting step i n the biosynthesis of catecholamines, Among the various mechanisms imp licated in the regulation of TH activity, alternative splicing of TH p rimary transcript has been described as a characteristic of higher pri mates and Drosophila. We investigated whether there is such a regulato ry mechanism in the rat. Reverse transcriptase-PCR experiments were pe rformed with RNA from PC12 cells. A new TH mRNA species was evidenced, resulting from the use of an alternative donor site in exon 2. RNase protection assays and in situ hybridization experiments detected this mRNA species in the adrenal medulla but not in the main catecholaminer gic nuclei of the CNS. The corresponding putative protein lacks 33 ami no acids in the N-terminal regulatory domain. A recombinant protein wa s produced in E. coli. Its in vitro specific activity was similar to t hat of the previously identified TH protein.