STRUCTURE, GENOMIC ORGANIZATION, AND EXPRESSION OF THE ARABIDOPSIS-THALIANA ACONITASE GENE - PLANT ACONITASE SHOW SIGNIFICANT HOMOLOGY WITH MAMMALIAN IRON-RESPONSIVE ELEMENT-BINDING PROTEIN

We report the purification of the unstable aconitase enzyme from melon needs and the NH2-terminal amino acid sequence determination. Antibodies raised against this protein enabled the first isolation and characterization of cDNA encoding aconitase in plants. A full-length cDNA clone of 3210 base pairs was isolated from a library of cDNA clones derived from immature pods of Arabidopsis thaliana. The amino acid sequence deduced from the open reading frame includes the sequence obtained by direct sequencing of the NH2 terminus of the purified enzyme. Genomic clones of the aconitase gene were isolated, and comparison of the cDNA ang genomic sequences reveals that the coding sequence is divided among 20 exons. There are five putative sites for transcription initiation. The aconitase gene is constitutively expressed, but at a low level, during most developmental stages, with a dramatic increase during seed and pollen maturation and during germination. Surprisingly, plant aconitases have reasonably high homology to binding proteins for iron-responsive elements from mammalian species, opening the possibility that a similar type of translational regulation occurs in plants.