Tryptophan absent, repressor inactive, operon on.
In the repressibletrpoperon,
5 genes
encoding the enzymes to synthesize tryptophan are regulated by a
promoter
and an operator.
When tryptophan is absent,
the repressor
(with its own promoter)
is inactive and the operon is on.
RNA polymerase attaches to the DNA at the promoter
and transcribes the operon's genes.
