Fur represses ryhB transcription .
In the absence of Fe and/or Fur , repression of ryhB is relieved , leading to negative regulation of ftnA .
In the absence of Fe and/or Fur , repression of ryhB is relieved , leading to negative regulation of bfr .
Fur activates sodB by repressing the expression of ryhB under high-iron conditions .
The expression of ryhB , in turn , is repressed by Fur under high-iron conditions .
Consequently , if Fur acts as a simple repressor of the factor , as it does with ryhB controlling sodB , then the Fur binding site must be far from consensus , leading to weak binding of Fur under normal laboratory conditions ; overproduction of Fur leads to further repression .
However , E. coli Fur is also known to activate the expression of many genes indirect mechanisms , the latter involving repression of a small regulatory RNA , ryhB .
However , E. coli Fur is also known to activate the expression of many genes direct mechanisms , the latter involving repression of a small regulatory RNA , ryhB .
Under iron-rich conditions , it has been shown that expression of ryhB gene is repressed by Fe2 + - Fur , whereas transcription of genes is elevated .
Fur repression of ryhB transcription is abated