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__NOTOC__ FourU thermometers are a class of non-coding RNA thermometers found in ''Salmonella''. They are named 'FourU' due to the four highly conserved uridine nucleotides found directly opposite the Shine-Dalgarno sequence on hairpin II (''pictured''). RNA thermometers such as FourU control regulation of temperature via heat shock proteins in many prokaryotes. FourU thermometers are relatively small RNA molecules, only 57 nucleotides in length, and have a simple two-hairpin structure.〔 FourU are found in the 5' untranslated region of the gene for heat shock protein ''Salmonella agsA'',〔〔(【引用サイトリンク】title=aggregation suppressing protein )〕 they repress translation of this protein by base-pairing the Shine-Dalgardo sequence of the gene's mRNA.〔 This prevents ribosomes from binding the gene's start codon. Other known RNA thermometers include the ROSE element and Hsp90 cis-reg element. ==Response to temperature== Hairpin II appears to be a dynamic feature of FourU's secondary structure.〔〔 It undergoes a conformational shift when exposed to temperatures above 45°C, becoming increasingly unpaired as temperature rises.〔 Hairpin I, in contrast, remains stably base-paired in temperatures as high as 50°C, which implies the structural shift of hairpin II from closed to open may have an important role in heat shock response.〔 A later study used mutant analysis and calculations of enthalpy and entropy to support a cooperative zipper-type unfolding mechanism of FourU hairpin II in response to temperature increase.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「FourU thermometer」の詳細全文を読む スポンサード リンク
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