Questions_Sigma_1

Questions_Sigma_1 - Questions for Sigma Factors and the...

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Unformatted text preview: Questions for Sigma Factors and the Control of Bacterial Transcription 1. Which of the following statements is not true: a) Sigma is a subunit of RNA polymerase. b) Sigma recognizes DNA sequence elements present in the promoters for genes. c) When sigma is part of RNA polymerase, this form of the enzyme is called core enzyme. d) Sigma is not part of RNA polymerase during the elongation phase of transcription. 2. Sigma-70 is considered the “housekeeping” sigma factor in comparison to the alternative sigma factors. The gene for sigma-70 [can/can not] be deleted. The genes for alternative sigma factors [can/can not] be deleted. 3. You want to determine whether the late flagellar gene fliC is expressed at higher levels in a wild-type strain versus a strain that has the gene for sigma-28 deleted. What method would you choose to monitor expression of fliC. 4. Late flagellar genes are not expressed in strains unable to assemble the basal body of the flagellum. Sigma-28 is required for expression of these genes. What affect do you predict deletion of the gene for FlgM (anti-sigma factor) to have on expression of these late flagellar genes. a) increased expression b) decreased expression c) unchanged expression 5. You want to know whether the levels of sigma-32 protein increase in cells grown at 42°C versus cells grown at 30°C. What method would use to measure the level of sigma-32 in cells? 6. You have identified a protein, PurR, that you believe to be a sigma factor that is necessary for transcription of purA in E. coli. You have purified PurR protein. What test would you perform to determine whether PurR is a sigma factor. 7. Synthesis of a peptide antibiotic by B. sillus requires expression of the gene pepT. A strain lacking the sigP gene does not transcribe pepT. The sigP gene codes for a protein that has similarity to sigma factors from other bacteria. Expression of pepT is OFF when the cells are grown rapidly in a rich medium, and expression of pepT is ON when the cells are grown slowly in a minimal medium. The sigP gene is the first gene in a two-gene operon with asfP. You hypothesize that asfP codes for an anti-sigma factor that inhibits SigP. A) Based on this hypothesis, what do you predict to happen to expression of pepT in strains that are deleted for asfP when grown in RICH medium relative to a wild-type strain? 1) Expression of pepT will be higher 2) Expression of pepT will be lower 3) Expression of pepT will be unchanged B) Based on this hypothesis, what do you predict to happen to expression of pepT in strains that are deleted for asfP when grown in MINIMAL medium relative to a wild-type strain? 1) Expression of pepT will be higher 2) Expression of pepT will be lower 3) Expression of pepT will be unchanged (either answer is acceptable) 8. You are studying how the bacterium, Rhodobacter capsulatus, responds to different oxygen concentrations. You find that the levels of a cytochrome oxidase protein, Oxy-1, decrease at low oxygen concentration. You further find that the levels of transcription of the gene encoding Oxy-1, oxyA, are lower at low oxygen concentration (see the graph below). You isolate a mutant of R. capsulatus that is defective in decreasing transcription of oxyA under low oxygen concentration conditions (see graph below). You find that this mutant has a mutation in a gene encoding a sigma factor, called sigma-L. Propose a model to explain how sigma-L regulates oxyA in response to oxygen. oxyA-lacZ transcriptional fusion 90 80 70 ß-galactosidase 60 specific activity 50 40 30 20 10 0 High Oxygen Low Oxygen Wild-Type . Sigma-L Mutant 9. Describe one criterion that you would use to distinguish whether a sigma factor is a housekeeping sigma factor versus a minor sigma factor. (Note: there is no need to propose an experimental plan here.) 10. (A) Propose an experiment to determine whether your favorite bacterium, Globus aquifex, is able to sense and adapt to acidic pH. Shown below is the growth rate of G. aquifex at different pH. (B) Describe or draw the expected results of your experiment if G. aquifex is able to sense and adapt to acidic pH. (C) Describe or draw the expected results of your experiment if G. aquifex is NOT able to sense and adapt to acidic pH. ...
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This note was uploaded on 03/06/2012 for the course MIMG 100 taught by Professor Lazazzera during the Summer '10 term at UCLA.

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