Structural organization of the rat branched-chain 2-oxo-acid dehydrogenase kinase gene and partial characterization of the promoter-regulatory region.

The gene encoding the rat branched-chain 2-oxo-acid dehydrogenase kinase (EC 2.7.1.115) has been isolated and partially characterized. The entire gene, including the promoter-regulatory region, spans 6 kb and contains 11 exons. The 5'-untranslated region comprising 264 bp is interrupted by intron 1 which is 581 bp in size. The complete in-frame sequence of intron 7 encodes the 49 amino acid insert previously reported to be present in the larger isoform of the rat kinase (Harris, Popov, Shimomura, Zhao, Jaskiewicz, Nanaumi and Suzuki (1992) Adv. Enzyme Regul. 32, 267-284). Sequencing of the 679 bp of the 5'-flanking region showed the absence of a canonical TATA box, similar to other branched-chain 2-oxo-acid dehydrogenase-complex genes. Several candidate cis-acting elements are present. These include CAAT boxes, Sp-1-binding sites, GCN-4 sites, CCAAT enhancer binding-protein sites (C/EBP) and glucocorticoid-responsive element (GRE) sites. Also present are a pair of direct repeats of unknown function. The luciferase-reporter assay showed that promoter activity is markedly higher in normal rat kidney (NRK-52E) cells than in rat hepatoma (FTO-2B) cells, and that the 5'-flanking region between bases -449 and +264 is both necessary and sufficient for basal transcription of the kinase gene.