STRUCTURE, GENOMIC ORGANIZATION, AND EXPRESSION OF THE ARABIDOPSIS-THALIANA ACONITASE GENE - PLANT ACONITASE SHOW SIGNIFICANT HOMOLOGY WITHMAMMALIAN 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. Antibod ies raised against this protein enabled the first isolation and charac terization of cDNA encoding aconitase in plants. A full-length cDNA cl one of 3210 base pairs was isolated from a library of cDNA clones deri ved from immature pods of Arabidopsis thaliana. The amino acid sequenc e deduced from the open reading frame includes the sequence obtained b y direct sequencing of the NH2 terminus of the purified enzyme. Genomi c clones of the aconitase gene were isolated, and comparison of the cD NA ang genomic sequences reveals that the coding sequence is divided a mong 20 exons. There are five putative sites for transcription initiat ion. The aconitase gene is constitutively expressed, but at a low leve l, during most developmental stages, with a dramatic increase during s eed 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 th at a similar type of translational regulation occurs in plants.