Cloning, sequencing, and transcriptional analysis of the gene coding for the vegetative sigma factor of Agrobacterium tumefaciens.

The sigA gene of Agrobacterium tumefaciens was cloned and sequenced. Comparison with previously analyzed sigA genes revealed a high degree of similarity in nucleotide and amino acid sequences of regions two, three, and four of vegetative sigma factors. However, the upstream regulatory region shows no sequence homology with the Escherichia coli heat shock (sigma 32) promoters. It also does not contain the hairpin-loop structure (inverted repeat sequence) that was found in the upstream region of the groE operon in A. tumefaciens. The transcription initiation site of the gene was determined and found to be at the same position during normal growth and under heat shock conditions. Furthermore, no heat shock activation was observed at the transcriptional level.