Characterization of FruR as a putative activator of the fructose operon ofSpiroplasma 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 e nhanced 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, ind icating that FruR is an activator of the fructose operon. The promoter of t he fructose operon was localized by primer extension, and a direct T-rich r epeat was found to overlap the -35 box. This repeat could be the binding si te of FruR. The presence of fructose in the culture medium also decreases t he toxicity of methyl a-glucoside. however FruR is not involved in this reg ulation. This is the first description of transcription regulation of a mol licute operon. (C) 2001 Federation of European Microbiological Societies. P ublished by Elsevier Science B.V. All rights reserved.