An Enhancer Element in the House-keeping Promoter for Acetyl-CoA Carboxylase Gene

The gene for acetyl-CoA carboxylase, the rate-limiting enzyme in the biogenesis of long chain fatty acids, contains two promoter regions which control the generation of different forms of carboxylase mRNA. At least five different forms of carboxylase mRNA are generated by differential splicing of the two transcripts formed under the influence of two promoters. One of the two promoters is mainly responsible for the generation of a class of carboxylase mRNA species, pAU type, induced tissue specifically under lipogenic conditions; the other generates ACC mRNAs (FL-type) which are expressed under normal conditions but this expression is also stimulated under lipogenic conditions. In the present studies, we have characterized the promoter that is responsible for the FL-type of ACC mRNA. This promoter contains no TATA or CAAT boxes, but five G/C motifs whose sequences are typical of transcriptional factor Sp1 binding sites. However, the presence of these G/C motifs is not sufficient to drive the transcription of the gene under the control of this promoter. Expression of promoter activity requires three copies of 11 to 13mer enhancer elements which are located in the region upstream to the G/C motifs. The presence of such enhancer elements in a house-keeping gene is unusual, and provides a new example where an enhancer element occurs in the CpG island-type promoter of a house-keeping gene.