The primary structure of acetyl-coenzyme A carboxylase messenger-RNA
Abstract
Acetyl-Coenzyme A Carboxylase (ACC; acetyl-CoA:carbon dioxide ligase (ADP forming), EC 6.4.1.2), is the biotin containing enzyme that catalyzes the regulatory step in the biosynthesis of fatty acids. The primary structure of ACC mRNA, and the structural and functional features thereby deduced, are described. ACC mRNA exists as a 10 Kb, very rare mRNA species in tissues engaged in lipogenesis. Biologically active ACC mRNA has been prepared from lactating rat mammary glands. ACC cDNA clones were generated from this RNA preparation and used to obtain the primary structure of ACC mRNA. ACC mRNA contains an open reading frame 7035 nucleotides long; it encodes a polypeptide of 2345 amino acids having a M$\sb{\rm r}$ of 265,220 dalton. The deduced protein exhibits the phosphorylation sites involved in the covalent modification of the enzyme, as well as the site for biotinylation, VMKM, which is located within the NH$\sb2$-terminal half of the encoded polypeptide. Sequence homologies between ACC and carbamyl phosphate synthetase, and between ACC and other biotin containing enzymes suggest that all the catalytic activities exhibited by ACC are contained in this polypeptide. This supports the hypothesis that this multifunctional enzyme has evolved through the gene fusion of separated catalytic units. Titration of the ACC gene copy number indicates that there is one copy of the ACC gene per haploid chromosome. Nonetheless, ACC mRNA exhibits a profuse 5$\sp\prime$ end heterogeneity. Five types of ACC mRNA having different 5$\sp\prime$ untranslated regions have been characterized. They are expressed in a tissue specific manner, and in the liver, two of them are synthesized in response to an induced lipogenic condition. Experimental evidence supports the hypothesis that the 5$\sp\prime$ end heterogeneity is the result of alternative promoter use and differential splicing of the ACC transcriptional unit.
Degree
Ph.D.
Advisors
Kim, Purdue University.
Subject Area
Biochemistry
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.