Structural features of the acetyl-CoA carboxylase gene: mechanisms for the generation of mRNAs with 5' end heterogeneity.

Acetyl-CoA carboxylase [acetyl-CoA:carbondioxide ligase (ADP-forming), EC 6.4.1.2] is the rate-limiting enzyme in the biogenesis of long-chain fatty acids. We have previously characterized five acetyl-CoA carboxylase mRNA species that differ in their 5' untranslated regions but not in the coding region. We have now characterized the exon-intron structure of the genomic DNA that encodes the 5' untranslated region of the mRNA. Generation of different forms of the mRNA is the result of the selective use of two promoters and differential splicing of five different exons. These five exons contain a total of 645 nucleotides and they are scattered over a 50-kilobase-pair genomic DNA region that we have characterized.