The E. coli tryptophan operon is subject to regulation by attenuation (10-fold)

Question

The E. coli tryptophan operon is subject to regulation by attenuation (10-fold) and transcriptional control (70-fold). The lacZ reporter gene shown below has been cloned into an E. coli low copy number plasmid vector. When this plasmid is transformed into an E. coli strain that has its lacZ gene encoding Beta-galactosidase deleted but is a wild type strain in all other respects unless indicated otherwise in the first column of the table below Note 1: The strain expresses about 1 unit of Beta-galactosidase in medium with lots of tryptophan. Note 2: That the trpR gene codes for the tryptophan repressor protein. Note 3: The figure below is reporter gene shows the two configurations that the leader region can assume trp operon promoter operator lacZ reporter trp leader region )Tryptophan starvation b) Trgtophan abundance Rbosome st2 No teminator polymerase continues Teminalor hain Figure 7.36 How much Beta-galactosidase will the combinations of E. coli strain and mutated reporter genes express under the growth conditions indicate? Relative levels of Beta-galactosidase expressed Genotype of E. coli strain trp-lacZ reporter gene plasmid Minimal medium with lots of tryptophan Minimal medium with no tryptophan lacZ AlacZ 1aeZ trpR 1aeZ 1aeZ trpR. AlacZ plasmid as shown above plasmid with region 1 of the leader region deleted plasmid as shown above plasmid with a trp Oc mutation plasmid with a trp Oc mutation Plasmid with the Shine Dalgarno sequence of the leader peptide gene deleted.

Explanation / Answer

Relative level of beta-galactosidase expressed

Minimal Medium with no tryptophan

Relative level of beta-galactosidase expressed

Minimal medium with lots of tryptophan

Genotype of E.coli strain trp-lacZ reporter gene plasmid

Relative level of beta-galactosidase expressed

Minimal Medium with no tryptophan

Relative level of beta-galactosidase expressed

Minimal medium with lots of tryptophan

Del lacZ Plasmid as shown above 1 unit of activity higher activity Del lacZ Plasmid with region 1 of the leader deleted low activity Higher activity Del lacZ trpR- Plasmid as shown above 1 unit of activity 1 unit of activity Del lacZ Plasmid with a trp O mutation high activity high activity Del lacZ trpR- Plasmid with a trp O mutation high activity high activity Del lacZ plasmid with Shine dalgarno sequence deleted No activty No activity

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