Characterization of FruR as a putative activator of the fructose operon of Spiroplasma citri.

The role of fruR, the first gene of the Spiroplasma citri fructose operon, was investigated. In vivo transcription of the fructose operon is greatly enhanced by the presence of fructose in the growth medium while glucose has no effect. When fruR is not expressed, transcription of the fructose operon is not stimulated by fructose, and fructose fermentation is decreased, indicating that FruR is an activator of the fructose operon. The promoter of the fructose operon was localized by primer extension, and a direct T-rich repeat was found to overlap the -35 box. This repeat could be the binding site of FruR. The presence of fructose in the culture medium also decreases the toxicity of methyl alpha-glucoside, however FruR is not involved in this regulation. This is the first description of transcription regulation of a mollicute operon.