Also incorporate into your answer the molecular

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AraC does both in the presence and the absence of arabinose. Also, incorporate into your answer the molecular mechanism (known as the "Light-switch mechanism") that changes the activity of AraC in response to arabinose availability. (8) Page 3, v1
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Microbial Genetics BIOL518 Exam 4 - Fall 2010 Name_____________________________________________________________________ 15: Numerous examples of genes regulated via two-component signal transduction systems have been described through out the course. Why are these systems important? Describe the general mechanism used by two-component signal transduction system proteins for gene expression regulation. Be specific (ie - provide details of the mechanism, cellular location, appropriate names, include important conserved residues and domains) but describe what is true of most members of two-component signal transduction systems. (16) Page 4, v1
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Microbial Genetics BIOL518 Exam 4 - Fall 2010 Name_____________________________________________________________________ Short Answer. Briefly but completely answer each of the following questions. The point value for each is parentheses. (24 points total) 16: The genes encoding the subunits of the cholera toxin are carried on a ________________________________ in the chromosome of the bacterium Vibrio cholera . (2) 17: ___________ ____ is a unique response regulator that can bind to Sigma S and inhibit activity when it is __________________ (think how response regulators are regulated and then decide the appropriate state) (4). 18: The two families of sigma factors are and . (2) 19: The differential expression of all of the genes encoded by an organism under various conditions (such as glucose +/-) can be determined by fluorescent or radioisotope measurement using ____________________________ profiling (2). 20: In the presence of both glucose and arabinose, expression of the araBAD operon will be ____________________________ . (2) 21: Class transcriptional activators (such as CAP for the lac promoter) bind around 60 nucleotides upstream of transcriptional start sites (~-60) and typically interact with subunit of RNA polymerase holoenzyme (4). 22: Unlike most response regulators of the Two-component sensor response regulator family of regulatory proteins, the NtrC protein has a third, middle, domain that is responsible for (two possibilities) ____________________________________. (2) Page 5, v1
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Answer Key for Test “Exam#4-2010.tst”, 12/6/10 No. in Q-Bank No. on Test Correct Answer 12 113 1 D 12 110 2 A, C 11 126 3 B 12 29 4 B 11 89 5 A 12 115 6 None of the above 12 101 7 A, C, D 12 114 8 A, C, D 12 40 9 B, C, D 12 91 10 A, B, D 11 118 11 A, B, C, D 11 125 12 B, D 12 12 13 A, B, C, D 11 74 14 --In the absence of arabinose, the N-terminal arm of AraC binds to the C-terminal domain of AraC (1) -- the upstream AraC monomer binds at araI (1) --and the downstream AraC monomer binds to araO2 at -280 (1) --the DNA between araO2 and araI forms a loop (1) --AraC can not contact RNAP, therefore expression from the araBAD promoter is fully off. (1) --In the presence of arabinose, the N-terminal arm of the AraC protein binds over the arabinose binding pocket in the N-terminal domain of AraC (1) --Both monomers of AraC can bind at araI (1) --and therefore AraC is in the correct position to activate araBAD transcription. (1) 12 5 15 (2) One of the primary mechanisms for bacteria to sense environmental changes and adjust gene expression accordingly.
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