A theoretical operon (amo) in E. coli contains
several structural genes encoding enzymes involved in the
biosynthesis of a particular amino acid. Unlike the lac
operon, in which the repressor gene is separate from the operon
itself, for the amo operon, the repressor gene is found
within the operon itself. When the end product amino acid is
present, it binds to the repressor, and this complex binds to the
operator, repressing the operon. In the absence of the amino acid,
the repressor fails to bind to the operator, and transcription
proceeds.
Characterize this operon, comparing it to the regulation of the
lac and trp operons. Be sure to discuss how
regulation is affected by having the repressor gene as part of the
operon. Then, consider the following mutations:
a) Mutation in the operator region;
b) Mutation in the promoter region;
c) Mutation in the repressor gene.
In each case, state whether the operon will be transcribed or not,
and describe how the mutation affects the regulation of the operon.
Compare each response to the equivalent situation in the
lac and trp operons.
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