Structural analysis of the TNIT4 genes encoding nitrilase-like protein from tobacco

Nitrilase (nitrile aminohydrolase, EC 3.5.5.1) catalyzes the hydrolysis of indole-3-acetonitrile (IAN) to indole-3-acetic acid (IAA). The Arabidopsis thaliana genome has four nitrilase genes (NIT1 to NIT4), while tobacco (Nicotiana tabacum) has only NIT4 homologs (TNIT4A and TNIT4B) and no NIT1 to NIT3 homologs. We have cloned the promoter region of TNIT4B and determined the transcriptional start sites which are the same sites in both TNIT4A and TNIT4B. The TNIT4 genes are expressed in various organs at low levels. The positions of the exon-intron splicing junctions in Arabidopsis NIT1 to NIT3 are completely conserved in TNIT4A.