However, when the activated form of repressor which is induced by the attachment of two tryptophan molecules become abundant, it will bind to the operator site and block RNA polymerase from binding to the promoter, thereby, repressing transcription and forming the first feedback loop.
Further regulation occurs in some operons: a molecule called an inducer can bind to the repressor, inactivating it; or a repressor may not be able to bind to the operator unless it is bound to another molecule, the corepressor.
The results of analytical ultracentrifugation demonstrate that TtgR forms stable dimers in solution, and that two dimers bind to the operator.
In the monomeric pathway monomers bind to the operator site and then recruit another monomer to form a dimer directly on the DNA.
For example, in the case of the Trp Operator of E. coli, the Trp-repressor does not bind to the Operator if it is not bound to Tryptophan.
These results clearly demonstrate that the effect of LacI on the virulence of S. enterica is independent of its ability to bind to the operator sequence.
Mutating Gln60 to Gly and inserting three extra glycines after 60th amino acid of LacI abolishes its ability to bind to the operator sequence without affecting its folding, assembly and inducer (IPTG) -binding property.
The regulatory protein coded by the regulator gene can bind to the operator.
At high zinc concentrations, Rv2358 does not bind to the operator site in front of the rv2358- furB operon and, as a consequence, zinc uptake is prevented by the regulatory action of FurB and an excess of zinc is pumped out of the cell.
Subsequently, Tc binds to the repressor (TetR2 bound to the operators or free) with high affinity.
