Relative luminescence in all the figures stands for the absolute 10-s luminescence Because the Fur protein is a repressor of transcription , it was expected that deletion of the fur box from the sdiA promoter would increase sdiA transcription .
We next examined transcription of the two Fur-repressed genes in the strain that carried deletions of the rstA and fur genes and harbored either the RstA expression plasmid or the plasmid vector ; analysis determined that the mRNA levels of fhuA and fhuF were similar to those in the fur deletion strain regardless of RstA expression ( Fig. 1B ) .
Iron depletion also eliminated the regulatory effect of RstA on the Fur-repressed genes : in bacterial cells grown in LB-medium containing the iron-specific chelator dipyridyl , the transcription levels of the fhuA and fhuF genes were increased to the levels observed in the fur deletion strain even when the RstA protein was overexpressed ( Fig. 1B ) .
We also determined that the Fur protein was acting as a transcriptional repressor of the feoAB operon because deletion of the fur gene resulted in a twofold increase of Fig. 2A .
We also determined that the Fur protein was acting as a transcriptional repressor of the feoAB operon because deletion of the fur gene resulted in a twofold increase of the wild-type feoAB transcripts .
Expression of each sRNA was also induced when fur was deleted , confirming the role of Fur as a repressor for both of these sRNAs .
Fur ( H90R ) production from the plasmid-linked lac promoter could no longer complement ssaG expression in the fur deletion strain under pH Fig. 2B , further that Fur repression of SPI-2 expression under acidic conditions is dependent on iron .
Fur ( H90R ) production from the plasmid-linked lac promoter could no longer complement ssaG expression in the fur deletion strain under pH 6.0 conditions , further that Fur repression of SPI-2 expression under acidic conditions is dependent on iron .
Therefore , Fur might indirectly repress tcf expression by repressing these sRNAs , as loss of fur in low iron concomitantly increases expression of both sRNAs .