Example of gene control in bacteria

The lactose operon on a bacterial chromosome.

The operon consists of a promoter flanked by two operators, and three genes for lactose-metabolizing enzymes.

What portion of the operon binds RNA polymerase when lactose is present?

1) The lac operon in the Lactose Operon E. coli chromosome.
2) In the absence of lactose, a repressor binds to the two operators. Binding prevents RNA polymerase from attaching to the promoter, so transcription of the operon genes does not occur.
3) When lactose is present, some is converted to a form that binds to the repressor. Binding alters the shape of the repressor such that it releases the operators. RNA polymerase can now attach to the promoter and transcribe the operon genes.