Unformatted text preview: g the protein.
But the mutant protein may not be fully functional.
Permease is defective
Lactose is nutrient
For both the initiator protein and RNA polymerase to bind, the DNA
sequences can’t overlap. If LacI had affinity for DNA in the presence of
lactose, no transcription would occur because in the lac operon, the P
and O do overlap. If LacI is bound, RNA polymerase is blocked from
binding. This operon wouldn’t inhibit gene expression in response to an
environmental signal, because transcription is only initiated in the
presence of the signal, when the initiator protein and RNA polymerase
bind. To ensure that the initiator protein is made, so that transcription of
the operon would be possible, the initiator protein must be made all the
time, but it doesn’t need to be transcribed in large amounts (see page
174), a few copies of the initiator protein would be sufficient....
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