Rola alternatywnych czynników sigma S (σS) i sigma B (σB) w odpowiedzi komórki bakteryjnej na stres oraz ich regulacja
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Bacteria successfully take possession of almost every recess of the earth. However bacteria can be liable to big changes of environmental conditions in every settled biotope. Some of them living in a high specializated medium do not show usually ability of tolerate others media than their most favourable. In case of changes of medium parameters some of bacteria start to migrate and look for others media securing them proper growth and development approximate optimum conditions. There are also bacteria which are able to survive in spite of changes happen in their direct environmental. Their survival competence is caused by the lack of susceptibility on specified medium changes or ability of adaptation to new conditions moreover by taking the profits from the medium. The tolerance and adaptation bacterial cells to different conditions which following in the nearest environmental result from cells response on stress factors. Precised signals coming from the medium cause in the cells a number of changes happen in genes expression regulated on transcription and translation level. The information coded in bacterial genome enable cells to produce many different proteins. However not all proteins are synthesized in the same time and the process of their synthesis is subject to strict control. Cells under stress synthesize proteins which secure them survival in untipical for their growing conditions. The main roles in this process play alternative sigma factors. Bacterial cells contain also general sigma factor (for example σ 70 in Escherichia coli, σ 43 in Bacillus subtilis) responsible for transcription most of the genes. However alternative sigma factors rarely regulate initiation of transcription. They are active only in case of cell stress conditions and also they take part in gene expression conected with the life cycle of the cell and stationary or exponential growth phase of bacteria. The most important function in stress conditions of E. coli plays an alternative sigma S (σ S, σ38) factor. Because of its regulatory function a lot of attention is dedicated to researches refer to σS in a recent time. Sigma B – which is one of the best known alternative sigma factors in Gram positive bacteria – plays a similar role to sigma S. Factor σ B functions as a general response regulator to stress in such bacteria as Bacillus, Staphylococcus and Listeria . These two alternative sigma factors: sigma S and sigma B often, if not always work in connection with others form of regulation. Bacteria show ability of detection many signals coming from the environment by means of sensors systems situated in cell envelope. Although σ S and σ B play the similar role in the cell they are controlled by completely different mechanisms.
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