A newly identified bacterial strain needs melrose as a growthfactor. To synthesize melrose these bacteria use three enzymes thatare encoded by the genes melA, melB andmelC in the mel operon. The expression of thesethree genes is controlled by a regulatory protein MelR. Melrosebinds to MelR, and it changes the ability of MelR to bind to theregulatory region of the mel operon.

The mel genes are expressedonly in the absence of melrose. The regulator MelR, only in theabsence of melrose, can bind at the regulatory region ofmel operon.

Answer all questions

1. Draw the mel operon showing structural and regulatorygenes, the regulatory region including the promoter and terminator.Describe the role of each term in your drawing.
2. Show the regulation model of the mel operon in thepresence of melrose. In your figures, include structural genes,regulatory region, MelR, melrose, transcription and translation.Describe the process of how gene expression is turned ON or OFF inthe presence of Melrose.
3. Show the regulation model of the mel operon in theabsence of melrose. In your figures, include structural genes,regulatory region, MelR, transcription and translation. Describethe process how gene expression is turned ON or OFF in the absenceof melrose.

d. Answer the following questions and provide an explanation foreach answer     

i. Is the mel operon inducible or repressible?

1. Is the MelR a positive or negative regulator?

1. Predict the expression of the mel operon in thefollowing three melR mutants melR1,melR2 and melR3. Choose an answer as regulated orconstitutive or no expression, including an explanation.

i. In a melR1 mutant, MelR has lost the ability to bindto melrose.

ii. In a melR2 mutant, MelR cannot bind to theregulatory region irrespective of the presence or absence ofmelrose.

1. In a melR3 mutant, MelR binds to the regulatory regionirrespective of the presence or absence of melrose.