Control of the lac operon

The three structural genes of the lac operon,
lacZ, lacY, and lacA, are controlled bymeans of a
repressor protein that binds to the promoter/
operator region (P–O). When the repressor is
bound to the P–O region, RNA polymerase cannot
bind to the promoter region. Transcription
is blocked (1), and the three gene products are
not formed.The lac operon is activated when a
!-galactoside molecule binds to one of the subunits
of the repressor (2) and inactivates it. RNA
polymerase can then bind to the promoter region
and transcription can begin.