Lac operon has three structural genes, z, y, and a. Within the induced operon, the structural genes transcribe a polycistronic mRNA that yields three enzymes. These are B-galactosidase (z-gene), which brings about hydrolysis of lactose to form glucose and galactose. Galactoside permease (y-gene) is required for the entry of lactose into the bacterium. Galactoside transacetylase (a-gene) can transfer the acetyl group from acetyl Co-A to B-galactoside.