THE RAT MITOCHONDRIAL 3-HYDROXY-3-METHYLGLUTARYL-COENZYME-A-SYNTHASE GENE CONTAINS ELEMENTS THAT MEDIATE ITS MULTIHORMONAL REGULATION AND TISSUE-SPECIFICITY

Mitochondrial 3-hydroxy-3-methylglutaryl-coenzyme-A HMG-CoA) synthase, a liver-specific enzyme, is a constituent of the HMG-CoA cycle respon sible for ketone-body synthesis. We report the isolation and character ization of genomic clones that encompass the gene for rat mitochondria l HMG-CoA synthase. The gene spans at least 24 kbp and contains ten ex ons and nine introns. The 5' flanking region of the gene has also been cloned and characterized. Exon 1 contains the untranslated sequence o f the transcript, extending downstream to enclose the coding region fo r the putative mitochondrial-targeting signal (35 amino acids). The 11 49-bp proximal region of the transcription start point permits transcr iption of a reporter gene in transfected hepatoma cells but not in an extrahepatic cell line, confirming the function of the promoter. A tru ncated construct of 142bp is still able to promote transcription in he patoma cells, suggesting the presence of liver-specific enhancer eleme nts in the proximal promoter region. The 5' flanking region contains t ypical promoter elements, including a TATA box and several putative re cognition sequences for transcription factors involved in controlling both basal-level and hormone-modulated transcription rates. Furthermor e, the presence in the mitochondrial HMG-CoA-synthase promoter of cis- elements, responsible for the multihormonal regulation of transcriptio n, is supported by transient transfection experiments.