C2005/F2401 '06 -- Recitation Problems #9 -- Hints

For these problems it usually helps to draw out all relevant DNA's and indicate all relevant genes for enzymes, repressors, operators, promotors, etc. Then, for each set of conditions, consider what repressor proteins will be made, what state the proteins will be in, which structural genes will be turned on (or off), etc.

A. What does it take for each operon to be fully "on?"

B. Try drawing the set up. What repressor is controlling production of enzyme X? (Note that there are no repressor genes on the plasmids.)

More hints for B:

Is production of enzyme X inducible, repressible or constitutive?

If you want the cells to stop making enzyme X, do you want the repressor to bind to the plasmid or not? What will it take to make the repressor "do the right thing?"

C-1. What repressor is controlling production of enzyme X this time? (Remember that there are no repressor genes on the plasmids.) Will the promotor and/or operator determine whether you get maximal production of enzyme X?

C-2. What determines the maximum rate of production of enzyme X? The promotor? The operator?

D. What is allowing the bacteria to grow in the presence of sillimycin, recombination or complementation? Be sure to draw the set up. (What do you need the sillimycin for??)

More hints for D:

D-1. & D-2. Do both plasmids have to be transcribed? If so, what must be added to the medium to allow both plasmids to be transcribed?

D-3. Can one molecule of mRNA (from plasmid 3 or plasmid 4) code for good enzyme X?

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