CREB2 (cAMP responsive element binding protein 2).  "RNA polymerase has a low affinity for the promotor of the lac operon unless helped by regulatory protein calles the cAMP receptor protein CRP [or CREB2], which binds to a site on the DNA next to the promotor.  The CREB2 molecules can attatch to the DNA only when associated cyclic AMP whose concentration in the cell rises when the glucose concentration falls.  If glucose is scarce, cAMP activates CRP [or CREB2], and the operon produces abundant mRNA for the lactose pathway.  But when glucose is present, cAMP is scarce, CRP [or CREB2] is unable to stimulate transcription"(Campbell 340).