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Reading_SigmaFactors - Sigma Factors and Bacterial...

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1 Sigma Factors and Bacterial Transcription Textbook Reading Pages 354-355 “ Promoters and Sigma Factors The points to be remembered from this text: Know what is the function of the sigma subunit of RNA polymerase. What is the function of the -10 and -35 sequences? What is the difference between sigma-70 (sigma-A) and alternative sigma factors? What is an anti-sigma factor? Know how FlgM inhibition of sigma-28 relieved to allow expression of late flagellar genes. Stress Response Many alternative sigma factors are involved in reprogramming gene expression in response to an environmental stress. A stress is defined as an abiotic factor(s) that limits the production of biomass. Examples of stress factors are unfavorable temperature, pH, water availability, and oxygen concentration. Adaptation to Stress Cells are capable of sensing and responding to stress. Alternative sigma factors are often part of the signal transduction pathways for responding to stress. A response to stress can be easily demonstrated by observing that bacteria that are exposed to a sublethal level of a stress factor are able to survive for longer periods of exposure to a lethal level of that stress factor than cells that were not exposed to the sublethal level of stress. Determining proteins induced in response to stress To determine which proteins are most highly transcribed and translated in cells, cells are incubated with a radioactive amino acid, 35 S-methionine, for a short period of time (e.g. 1 minute). Only proteins that are being synthesized in that short period of time are become radioactive. After that short period of incubation, lyse (i.e. break) the cells. The proteins of the cells can then be separated based on size by SDS-PAGE (SDS-polyacrylamide gel electrophoresis). If the SDS-polyacrylamide gel is exposed to film, you will see the number and location (i.e. size) of the labeled proteins. Fig. 1 shows proteins that are synthesized during Textbook Reading Pages 352-353 “ Steps in RNA Synthesis The points to be remembered from this text: Know that there are promoters and terminators that determine the start and end points of transcription. Know of what core RNA polymerase is comprised. Know what is the function of core RNA polymerase. Know of what holo RNA polymerase is comprised. Know what is the function of the holo form of RNA polymerase.
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2 growth of Escherichia coli cells to 42°C, a sublethal temperature stress, as compared to those synthesized in cells grown at 30°C . Note that only the proteins synthesized at the highest rate are observed by this method. Additional methods that will not be covered are needed to identify the proteins that were radiolabelled. Chaperones and Proteases Heat shock proteins (proteins induced by high temperature stress) were found to be chaperones and proteases. Chaperones aid in the folding of proteins or keep proteins unfolded to be degraded by proteases. Both chaperones and proteases limit the damaging effects of unfolded proteins that occur at higher temperatures.
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