For each of the E. coli strains below, determine the effect of the genotype on e

Question

For each of the E. coli strains below, determine the effect of the genotype on expression of the trpE and trpC genes in the presence and absence of tryptophan. In the wild-type strain (genotype: R+ P+ O+ att+ trpE+ trpC+), the trpE and trpC genes are fully induced in the absence of tryptophan and fully repressed in the presence of tryptophan.

Key:

R = functional repressor gene; Rn = product cannot bind tryptophan; R- = product cannot bind operator

O = functional operator; O- = operator cannot bind repressor protein

att = functional attenuator; att- = a deletion of the attenuator sequence

P = functional promoter; P- = a deletion of the trp operon promoter

trpE- and trpC- = produce non-functional protein products

1) R+ P- O+ att+ trpE+ trpC+

2) R- P+ O+ att+ trpE+ trpC+

3) Rn P+ O+ att+ trpE+ trpC+

4) R- P+ O+ att- trpE+ trpC+

5) R+ P+ O- att+ trpE+ trpC- / R- P+ O+ att+ trpE- trpC+

6) R+ P- O+ att+ trpE+ trpC- / R- P+ O+ att+ trpE- trpC+

7) R+ P+ O- att- trpE+ trpC- / R- P+ O- att+ trpE- trpC+

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (-), trpC (-); No Trp = trpE (+), trpC (+)

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (-), trpC (-); No Trp = trpE (+), trpC (+)

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (-), trpC (-); No Trp = trpE (-), trpC (-)

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (-), trpC (-); No Trp = trpE (-), trpC (+)

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (+), trpC (-); No Trp = trpE (+), trpC (+)

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (+), trpC (+); No Trp = trpE (+), trpC (+)

      -       1.       2.       3.       4.       5.       6.       7.      

Trp = trpE (-), trpC (-); No Trp = trpE (+), trpC (+)

Explanation / Answer

1) R+ P- O+ att+ trpE+ trpC+

trpE and trpC is continuously synthesized even in the presence or absence of tryptophan.

2) R- P+ O+ att+ trpE+ trpC+

trpE and trpC is continuously synthesized even in the presence or absence of tryptophan.

3) Rn P+ O+ att+ trpE+ trpC+

trpE and trpC is continuously synthesized even in the presence or absence of tryptophan.

4) R- P+ O+ att- trpE+ trpC+

trpE and trpC is continuously synthesized even in the presence or absence of tryptophan.

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