PS08 - used for counterselection the number of h tet-r...

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P ROBLEM S ET 8 D UE : 3 N OVEMBER 2011 1. Two E. coli genes, A , and B , are known from mapping experiments to be very close together. A deletion mutation is isolated that eliminates the activity of both A and B . Neither the A nor the B protein can be found in the mutant, but a novel protein is isolated in which the amino-terminal 30 amino acids are identical to those of the B gene product, and the carboxyl terminal 30 amino acids are identical to those of the A gene product. a. With regard to the 5’ to 3’ orientation of the nontranscribed DNA strand (i.e. the coding strand), is the order of the genes AB or BA ? b. Can you make any inference about the number of bases deleted? 2. An Hfr strain transfers genes in alphabetical order. When tetracycline sensitivity is
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Unformatted text preview: used for counterselection, the number of h+ tet-r colonies is 1000-fold lower than the number of h+ str-r colonies found when streptomycin sensitivity is used for counterselection. Suggest an explanation for the difference. 3. You find a mutant strain of E. coli that produces betagalactosidase and permease constitutively. List the two mutations that could cause this phenotype. 4. Given the two mutations you listed in #3, what experiment could you use to distinguish between them? Explain how you would know which mutation was which (i.e., predict the outcome of your experiment for each mutation). Be brief (bullet points are fine)....
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