Inductors and regulatory properties of the genomic island-associated fru metabolic operon of Streptococcus agalactiae.

The fru metabolic operon of Streptococcus agalactiae encodes the phosphoenolpyruvate:carbohydrate phosphotransferase system (PTS) enzyme II complex Fru (EIIB , EIIA , and EIIC ); Fru R, a transcriptional activator with PTS regulatory domains (PRDs); a d-allulose-6-phosphate 3-epimerase; a transaldolase; and a transketolase. We showed that the transcription of fru is induced during the stationary phase of growth in complex media and during incubation in human cerebrospinal or amniotic fluids. d-allose and d-ribose are environmental signals governing this induction. PTS is involved in the activation of the fru promoter, and the histidine-67 of EIIA and the cysteine-9 of EIIB are important for this function. The activation of fru is also controlled by Fru R. The histidine-243 in the PRD domain, the histidine-323 in the PRD domain, the cysteine-400 in the EIIB-like domain, and the histidine-549 in the EIIA-like domain are important for the function of Fru R. Fru R binds to a DNA region containing palindromic sequences upstream of the identified transcriptional start site. EIIB interacts physically with the C-terminal part of Fru R (expressing the EIIB-like and EIIA-like motifs) and with EIIA . We propose a model of regulation of fru depending on the presence of an activatory carbohydrate in the growth medium.