Question

What is the likely effect of each of the following mutations of the trpL region on attenuation control of trp operon gene transcription? Explain your reasoning.

a. Region 3 is deleted.
b. Region 4 is deleted.
c. The entire trpL region is deleted.
d. The start (AUG) codon of the trpL polypeptide is
deleted.
e. Two nucleotides are inserted into the trpL region
immediately after the polypeptide stop codon.
f. Twenty nucleotides are inserted into the trpL region
immediately after the polypeptide stop codon.
g. Ten nucleotides are inserted between regions 2 and
3 of trpL.
h. Two nucleotides are inserted immediately following the
polypeptide start codon.
i. The entire polypeptide coding sequence of trpL is
deleted.
j. The eight uracil nucleotides immediately following
region 4 are deleted.

Answer 1

a. Region 3 is deleted.-- Attenuation cannot occur, because this region is transcription termination.
b. Region 4 is deleted. .-- Attenuation cannot occur, because this region is transcription termination.
c. The entire trpL region is deleted. .-- Attenuation cannot occur.

d. The start (AUG) codon of the trpL polypeptide is
deleted. .-- Attenuation cannot occur.

e. Two nucleotides are inserted into the trpL region immediately after the polypeptide stop codon. -—no effect on attenuation, because the correct sequence of trpL is not affected.

f. Twenty nucleotides are inserted into the trpL region immediately after the polypeptide stop codon. -- Attenuation is likely to be affected to some extent, because the correct sequence of trpL is not affected but somehow the more number of addition of nucleotides may effect.

g. Ten nucleotides are inserted between regions 2 and 3 of trpL.-- There is no effect on attenuation, because the enzyme transcribe the inserted nucleotide and terminates at region4.

h. Two nucleotides are inserted immediately following the polypeptide start codon.-- Attenuation cannot occur, initiation also not takes place.

i. The entire polypeptide coding sequence of trpL is deleted. –initiation and Attenuation cannot occur, because no initiation codons no start of transcription.

j. The eight uracil nucleotides immediately following region 4 are deleted.-- Attenuation cannot occur, because this region is transcription termination.