Characterization of the auxin synthesis genes of Erwinia herbicola pv. gypsophilae

We present the DNA sequence of some 3590 base pairs from the virulence plasmid of the crown-gall-forming bacterium Erwinia herbicola pv. gypsophilae strain PD713. This region includes the entire transcription unit of an operon encompassing the IAA synthesis genes. These genes, designated iaaM and iaaH, reside on a 78-MDa native plasmid. The sequence analysis indicates that the operon contains two open reading frames of 562 (iaaM) and 460 amino acids (iaaH), corresponding to proteins with molecular weight of 62,473 and 49,300 daltons, respectively. When cloned and expressed in minicell-producing E. coli, this sequence encodes production of two proteins, 49 and 62 kDa. Both genes show moderate to high homology to IAA synthesis genes from other plant-associated bacteria. Analysis by primer extension of the transcription initiation site located it 63 bases upstream of the translation initiation codon.