On 2015 Apr 10, Martine Crasnier-Mednansky commented:

According to Bledig SA, 1996, deletion of FruR (Cra) resulted in an appreciable increase of pykF-encoded pyruvate kinase synthesis on gluconeogenic carbon sources as compared to glycolytic carbon sources (casamino-acids were added to the culture medium to allow gluconeogenic growth). In addition, overexpressed FruR repressed the transcription of the pykF gene significantly on gluconeogenic carbon sources but not on glycolytic carbon sources. Thus the FruR (Cra) effect on pykF transcription significantly takes place under conditions of gluconeogenic growth. Therefore using pykF as a reporter gene for analyzing, under glycolytic growth conditions, a transcriptional regulation by FBP/Cra appears inappropriate. In addition, the concentration of FBP is dependent on the concentration of PEP because phosphofructokinase is subject to allosteric control by PEP Blangy D, 1968. Therefore decreasing pyruvate kinase synthesis below physiological level also decreases the FBP concentration which is in conflict with the present data (see Fig. S1 and Fig. 2B).

As shown in Fig. 1C, concentrations of FBP controlling the glycolytic flux are below 1 mM. This concentration range has been reported to be insufficient for FBP to displace FruR from its operator sites. In addition, cAMP-dependent carbon catabolite repression was reported by Nanchen A, 2008 to be the dominant control mechanism of metabolic fluxes under glucose limitation condition (used in Fig. 1B, black squares).

On 2015 Apr 10, Martine Crasnier-Mednansky commented:

According to Bledig SA, 1996, deletion of FruR (Cra) resulted in an appreciable increase of pykF-encoded pyruvate kinase synthesis on gluconeogenic carbon sources as compared to glycolytic carbon sources (casamino-acids were added to the culture medium to allow gluconeogenic growth). In addition, overexpressed FruR repressed the transcription of the pykF gene significantly on gluconeogenic carbon sources but not on glycolytic carbon sources. Thus the FruR (Cra) effect on pykF transcription significantly takes place under conditions of gluconeogenic growth. Therefore using pykF as a reporter gene for analyzing, under glycolytic growth conditions, a transcriptional regulation by FBP/Cra appears inappropriate. In addition, the concentration of FBP is dependent on the concentration of PEP because phosphofructokinase is subject to allosteric control by PEP Blangy D, 1968. Therefore decreasing pyruvate kinase synthesis below physiological level also decreases the FBP concentration which is in conflict with the present data (see Fig. S1 and Fig. 2B).

As shown in Fig. 1C, concentrations of FBP controlling the glycolytic flux are below 1 mM. This concentration range has been reported to be insufficient for FBP to displace FruR from its operator sites. In addition, cAMP-dependent carbon catabolite repression was reported by Nanchen A, 2008 to be the dominant control mechanism of metabolic fluxes under glucose limitation condition (used in Fig. 1B, black squares).