Catabolite repression allows microorganisms to adapt quickly to a preferred (rapidly metabolizable) carbon and energy source first.
This is usually achieved through inhibition of synthesis of enzymes involved in catabolism of carbon sources other than the preferred one.
However, the term "glucose effect" is actually a misnomer since other carbon sources are known to induce catabolite repression.
There are different catabolite-specific EIIA in a single cell, even though different bacterial groups have specificities to different sets of catabolites.
Next, bacteria start to transcribe the lac operon and produce β-galactosidase enzymes for lactose metabolism.
It works by the fact that Hpr is phosphorylated by a specific mechanism, when glucose enters through the cell membrane protein EIIC, and when Hpr is phosphorylated it can then allow CcpA to block transcription of the alternative sugar pathway operons at their respective cre sequence binding sites.