Isolation and characterization of the rat tryptophan oxygenase gene

Tryptophan oxygenase (TO, EC 1.13.1.12) from rat liver is subject to glucocorticoid and developmental control. To study the mechanism of regulation, TO mRNA sequences and the chromosomal TO gene were cloned. From a cDNA library prepared from rat liver poly(A)+ RNA enriched for TO mRNA, a recombinant plasmid containing TO cDNA sequences was identified by translation of hybrid-selected RNA and immunoprecipitation with antibodies directed against TO. This cDNA clone hybridizes to a mRNA 2000 bases long that is inducible by dexamethasone. With this clone as probe we isolated from a bacteriophage lambda rat DNA library genomic clones which together span a region of 32 kilobase pairs (kb). Heteroduplex analysis revealed that the gene extends over 19 kb and is interrupted by at least 11 introns. To characterize the presumptive control region the DNA sequence around the 5' end of the TO gene was determined. S1 nuclease protection experiments revealed two separate start sites for TO mRNA transcription within this region.