Single nucleotide resolution of sterol regulatory region in promoter for 3-hydroxy-3-methylglutaryl coenzyme A reductase

Sterol-dependent regulation of the 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase promoter was previously localized to a 42-base pair region containing an octamer sequene, referred to as the sterol regulatory element (SRE-1). A similar motif is found in the region of DNA that is required for sterol-dependent regulation of the HMG-CoA synthase and low density lipoprotein receptor genes. Single nucleotide substitution analyses of the low density lipoprotein receptor and HMG-CoA synthase promoters confirmed that the SRE-1 is an important sterol regulatory motif. In the current studies, a series of single nucleotide mutations were introduced into the HMG-CoA reductase regulatory region and transfected into Chinese hamster ovary cells. RNA produced by each mutant promoter was then measured in the presence or absence of sterols. Thirty-seven independent mutations were analyzed, and two separate domains were identified as being critical. One essential region was spread over 10 bases and contained half of the SRE-1; however, the other half of the SRE-1 was not important for sterol regulation. The second essential region spanned four contiguous bases. These two critical elements are separated from each other by three nones-ential bases. The results are interpreted to suggest that regulation of HMG-CoA reductase gene transcription by sterols requires additional or possibly separate factors from those required for sterol regulation of the low density lipoprotein receptor and HMG-CoA synthase promoters.