When arabinose is absent, the AraC protein acts as a negative regulator.
AraC acts as a dimer, and causes the DNA to loop. Looping brings the I1 and O2 sites in proximity to one another.
One AraC monomer binds to I1 and a second monomer binds to O2.
Binding of AraC prevents RNA Pol from binding to the PBAD promoter