STRUCTURE OF THE GENE ENCODING NITRILASE-1 FROM ARABIDOPSIS-THALIANA

The nitrilases of Arabidopsis thaliana (At) catalyze the conversion of indole-3-acetonitrile (IAN) to indole-3-acetic acid (IAA), thus contr olling the last step of auxin biosynthesis. A full-length genomic clon e encoding the complete cluster of the At nitrilases 1 to 3 (NIT1-3), including the respective promoter regions, has been isolated and the N IT1 isoform has been sequenced. The coding region (nit1) spans about 2 .3 kb and is composed of five exons separated by four introns. The exo n-intron splice junctions agree with the consensus sequences typical f or plant genes. In agreement with the known cDNA sequence, the exons e ncode a protein of 346 amino acids (aa) with a deduced molecular mass of 38.2 kDa. The transcription start point (tsp) of nit1 was determine d by primer extension experiments. This tsp defines a 5' untranslated region of 36 bp and is located 32 bp downstream from a TATA box. The p romoter region of nit1 is located within the approx. 1.5-kb intergenic part that separates the nit2 and nit1 coding sections.