Consider a hypothetical E. coli mutant that contains a
single nucleotide substitution in the trp leader region. The
mutation converts a codon for glutamic acid into a stop codon at
the position indicated in the figure below.
Assume that strain 401 also contains a mutation in the gene for
the Trp aporepressor that abolishes its ability to bind tryptophan
and therefore cannot perform the function of the Trp holorepressor.
Answer the following questions about how the mutations in strain
401 will affect the regulation of the trp operon.
Specifically:
(i) How will the events that are shown above in panel B for the
wild type trp attenuator, differ in the mutant? Use the
format of the tables below to express your answers on your answer
sheets:
(ii) Compare strain 401 with wildtype with respect to the
expression of the Trp operon under different culture conditions.
Specifically: how will the mutation affect the expression of the
enzymes of the trp operon when tryptophan is abundant and
when it is scarce? Once again, use the format of the tables below
to express your answers on your answer sheets:
UAG (a) trp leader RNA Translation GAG start codon 100 50 (b) Translation of trp leader High tryptophan RNA Ribosome covers region 2 3-4 stem-loop orms 140 Low tryptophan 2-3 stem- loop forms Ribosome is stalled at Trp codons in region 1 RNA polymerase continues transcription
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