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 sequence, 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 nonessential 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.