The lactase is an enzyme in the small intestine that breaks lactose into simpler sugar forms (galactose and glucose) that can be absorbed to generate energy. That sugar is important for gene regulation because it is linked to the Lac operon, the repressor for this structure prevents the DNA transcription, if the repressor is not in place the operon works and the enzyme is produced, being the lac repressor innately active in the absent of lactose.
