Fur 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 1. 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.

Control of lacI expression with a Fur-regulated promoter

Our iron sensor results showed that the Fur-regulated promoter of aceB represses expression of its target gene in response to iron. To create a fur inverter that activates expression in response to iron, we first linked the aceB promoter to the lacI gene.

NAME	FIGURE	Description
Promoter		Fur-regulated aceB promoter
LacI LVA		LacI repressor
Terminator		transcription stop signal
Plasmid		Backbone with ampicillin resistance

Table 1. Genetic elements used to make an inverter system.