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. In the absense of LacI the reporter is expressed. Thus, reporter expression is positively correlated with iron concentration.