Team:PennState/diauxie/TheSystem

Diauxie Elimination

Introduction

The System

Strategies

Progress

Conclusions

Parts

References

NHR Biosensors

NHR Introduction

Phthalate Biosensor

BPA Biosensor

In wild-type E. coli the xyl operon controls xylose transport and metabolism.

• The left facing xylAB genes code for xylose isomerase and kinase.
• The other set of genes, xylFGH are right facing and code for active xylose transport proteins.
• A bidirectional operator is necessary because of the opposite directions of transcriptional control for xylAB and xylFGH.
• XylR is located downstream of xylH but is controlled by its own weak promoter and is involved in regulation. Transcription is initiated when the protein XylR binds to xylose; this complex then binds to the XylR binding site located at both ends of the operator.

The system also requires binding of the activated complex cAMP-CRP (Cyclic adenosine monophosphate - cAMP Receptor Protein) to the individual CRP binding site to activate transcription. In terms of circuits, XylR and cAMP-CRP are the two inputs for this “and” logic gate. The protein cAMP is an indicator of the glucose concentration in the cell and becomes more abundant with glucose depletion. Another protein called XylE is a passive xylose transporter and exists elsewhere in the E. coli chromosome. Over expression of the xylE gene may help xylose enter the cell and begin its metabolism cycle.

Natural Operation - PN plasmid (see Implementation)

The presence of xylose and the absence of glucose are required for natural transcriptional activation in the xyl operon. Our goal was to have activation only dependent on the presence of xylose, independently of glucose.