STRUCTURE AND EXPRESSION OF AN ARABIDOPSIS ACETYL-COENZYME-A CARBOXYLASE GENE

Acetyl-coenzyme A carboxylase (ACCase) catalyzes the formation of malo nyl-coenzyme A, which is used in the plastid for fatty acid synthesis and in the cytosol for several pathways including fatty acid elongatio n and flavonoid synthesis. Two overlapping Arabidopsis genomic clones were isolated and sequenced to determine the entire ACCase-coding regi on. Thirty introns with an average size of 94 bp were identified by co mparison with an alfalfa ACCase cDNA sequence. The 10-kb Arabidopsis A CCase gene encodes a 251-kD polypeptide, which has 80% amino acid sequ ence identity with alfalfa ACCase and about 40% identity with ACCase o f rat, chicken, yeast, and the diatom Cyclotella. No chloroplast trans it peptide sequence was observed, suggesting that this Arabidopsis gen e encodes a cytosolic ACCase isozyme. ACCase gene transcripts were det ected by RNase protection assays in Arabidopsis root, leaf, silique, a nd seed. Genomic DNA blot analysis revealed the presence of a second r elated Arabidopsis ACCase gene.