Team:Jilin China/Background
Overview
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Sensing and responding to temperature is essential for bacterial survival
There are always challenges for bacterial survival, especially to keep suitable living status facing fluctuations of chemical and physical parameters. The common chemical perturbations include sudden deprivation of nutrients or key metabolites and changes in surrounding pH. And the most representative physical deviation is temperature shift. But in most cases, the ambient temperature change is more essential for bacterial life cycle than chemical parameters, due to the efficiency of all cellular processes is temperature dependent, especially the expression of any given gene. Therefore, it’s indispensable for bacteria to evolve effective strategies , which can respond to temperature forwardly before the damages such as unfolded proteins or membrane rigidification occur.
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Biological signal transduction systems that detect temperature shifts
When it comes to the biological behavior of temperature sensing, it’s very important to elicit a proper response that could coordinate the expression of temperature-relevant genes. The common detecting systems in bacterial cells are based on three manners as following:
1.Transcriptional level
Temperature sensing through DNA involves local DNA topological change followed by transcriptional event. For example, the thesis of transcription factorσ32 in E.Coli increases rapidly when temperature upshift, which could mediate the transcription of genes that haveσ32 -recognizing promoters. But this regulatory pathway takes some time to come into effect because the thermosensing proteins required time for upregulation.
2.Translational level
Temperature sensing also bases on many types of thermoregulatory RNA elements, also known for RNA-based thermosensors(RTSs), which are located in the 5’ untranslated region(5’ UTR) of mRNA. The 5’ UTR is a part of bacterial transcript of gene, which would not be translated into peptide. Therefore, RTSs are none-coding RNA elements. These types of thermoregulation respond to temperature and modulate the translation of already existing or nascent mRNAs, which could induce altered mRNA stability and ribosome accessibility of ribosome binding site(RBS) thereby controlling the translation efficiency.
3.Post-translational level
Unfolded or incorrect protein conformation is the most example of the consequences of temperature-induced damages. When temperature upshifts, chaperone proteins that are overexpressed can promote nascent polypeptide chains to fold into correct conformation, which is known as post-translational thermoregulation. But this process is more similar to lock the barn door after the horse was stolen, meaning cellular processes have already been altered due to temperature shifts.
