Team:PennState/diauxie/overview

The system

In wildtype E. coli the xyl operon controls xylose metabolism. The genes xylAB code for xylose isomerase and kinase, and the genes xylFGH code for active xylose transport proteins. Another protein called XylE, a passive xylose transporter, exists elsewhere in the chromosome. A bidirectional operator controls transcription in both the direction of xylAB and xylFGH. Transcription is initiated when the protein XylR binds to xylose which is followed by binding to the XylR binding site located at both ends of the operator. The binding of CRP-cAMP to a single CRP binding site is also required for activation. cAMP is an indicator of the glucose concentration in the cell and only becomes present when glucose is depleted.

In can be seen that both the presence of xylose and the absence of glucose are naturally required for transcriptional activation, our goal was to make only the presence of xylose necessary.