Oh, Lac Operon, gene cluster great, you code for enzymes three,
but only if Lactose in the cell arrives to set you free.
Lac Z, Lac A, Lac Y: these genes would be expressed
yet a crafty protein from gene I keeps you so repressed.
Binding to the Operator, I’s Repressor keeps you capped.
Do not despair—Lactose saves you from this cruel Repressor trap,
for Lactose turns the Repressor off, giving you the space
to make galactosidase, transacetylase, and lactose permease.
Then Polymerase binds the Promoter, and the Lac genes have their day.
yet alas! They break down Lactose, taking your savior away.
When Lactose is gone, the Repressor binds and causes you to freeze,
so Operon, to live again, you must find more milk and cheese.