The catabolite gene activator protein (CAP) is a transcription factor used by the bacterium E. coli in glucose-starvation conditions to recruit genes to allow it to metabolize the alternative food source lactose. CAP (rendered in oranges/purples) accomplishes this task by binding to a specific promoter region of DNA (blue) to aid the attachment of RNA polymerase (not shown) , which begins transcribing adjacent genes that code for enzymes needed for lactose metabolism.