Inverter

Normally, the Ferric Uptake Regulator (Fur) binds iron to repress transcription of its target genes. However, we needed a system that activates gene expression in response to iron. We thus constructed a "genetic invertor" system that reverses the Fur-regulatory system so that it indirectly activates gene expression in response to iron (Fig 1). This system consists of a Fur-regulated lacI gene and a LacI regulated reporter gene. When Fur binds iron, it represses expression of the LacI repressor which, in turn, permits expression of the reporter gene. Thus, reporter expression is positively correlated with iron concentration.

Fig Iron-responsive genetic inverter. The iron-Fur complex binds to the Fur site, here in the aceB promoter, to repress transcription of the lacI gene. In the absence of LacI, the RFP reporter is expressed.