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 responsible for ketone‐body synthesis. We report the isolation and characterization of genomic clones that encompass the gene for rat mitochondrial HMG‐CoA synthase. The gene spans at least 24 kbp and contains ten exons and nine introns. The 5′ flanking region of the gene has also been cloned and characterized. Exon 1 contains the untranslated sequence of the transcript, extending downstream to enclose the coding region for the putative mitochondrial‐targeting signal (35 amino acids). The 1149‐bp proximal region of the transcription start point permits transcription of a reporter gene in transfected hepatoma cells but not in an extrahepatic cell line, confirming the function of the promoter. A truncated construct of 142 bp is still able to promote transcription in hepatoma cells, suggesting the presence of liver‐specific enhancer elements in the proximal promoter region. The 5′ flanking region contains typical promoter elements, including a TATA box and several putative recognition sequences for transcription factors involved in controlling both basal‐level and hormone‐modulated transcription rates. Furthermore, the presence in the mitochondrial HMG‐CoA‐synthase promoter of cis ‐elements, responsible for the multihormonal regulation of transcription, is supported by transient transfection experiments.