BACKGROUND Translation of an mRNA in eukaryotes starts at an AUG codon in most cases, but near-cognate codons (NCCs) such as UUG, ACG, and AUU can also be used as start sites at low levels in Saccharomyces cerevisiae. Initiation from NCCs or AUGs in the 5'-untranslated regions (UTRs) of mRNAs can lead to translation of upstream open reading frames (uORFs) that might regulate expression of the main ORF (mORF). Although there is some circumstantial evidence that the translation of uORFs can be affected by environmental conditions, little is known about how it is affected by changes in growth temperature. RESULTS Using reporter assays, we found that changes in growth temperature can affect translation from NCC start sites in yeast cells, suggesting the possibility that gene expression could be regulated by temperature by altering use of different uORF start codons. Using ribosome profiling, we provide evidence that growth temperature regulates the efficiency of translation of nearly 200 uORFs in S. cerevisiae. Of these uORFs, most that start with an AUG codon have increased translational efficiency at 37 °C relative to 30 °C and decreased efficiency at 20 °C. For translationally regulated uORFs starting with NCCs, we did not observe a general trend for the direction of regulation as a function of temperature, suggesting mRNA-specific features can determine the mode of temperature-dependent regulation. Consistent with this conclusion, the position of the uORFs in the 5'-leader relative to the 5'-cap and the start codon of the main ORF correlates with the direction of temperature-dependent regulation of uORF translation. We have identified several novel cases in which changes in uORF translation are inversely correlated with changes in the translational efficiency of the downstream main ORF. Our data suggest that translation of these mRNAs is subject to temperature-dependent, uORF-mediated regulation. CONCLUSIONS Our data suggest that alterations in the translation of specific uORFs by temperature can regulate gene expression in S. cerevisiae.

中文翻译：

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酿酒酵母上游开放阅读框翻译的温度依赖性调节。

背景技术在大多数情况下，真核生物中mRNA的翻译起始于AUG密码子，但是近同源密码子（NCC）（例如UUG，ACG和AUU）也可以用作酿酒酵母中低水平的起始位点。来自mRNA的5'非翻译区（UTR）中的NCC或AUG的启动可导致上游开放阅读框（uORF）的翻译，其可能调节主要ORF（mORF）的表达。尽管有一些间接证据表明uORF的翻译可能受环境条件的影响，但对其生长温度变化的影响知之甚少。结果使用报告基因分析，我们发现生长温度的变化会影响酵母细胞中NCC起始位点的翻译，提示通过改变不同uORF起始密码子的使用可以通过温度调节基因表达的可能性。使用核糖体分析，我们提供证据表明生长温度调节酿酒酵母中近200 uORF的翻译效率。在这些uORF中，大多数以AUG密码子开头的uORF在37°C时相对于30°C时具有更高的翻译效率，而在20°C时则具有较低的翻译效率。对于始于NCC的翻译调控uORF，我们没有观察到调控方向随温度变化的一般趋势，这表明mRNA特异性特征可以决定温度依赖性调控的模式。与此结论相符，uORF在5'领导者相对于5'领导者中的位置 -cap和主要ORF的起始密码子与uORF翻译的温度依赖性调节的方向相关。我们已经确定了几种新颖的情况，其中uORF翻译的变化与下游主要ORF的翻译效率的变化成反比。我们的数据表明，这些mRNA的翻译受温度依赖性，uORF介导的调控。结论我们的数据表明，温度改变特定uORF的翻译可以调节酿酒酵母中的基因表达。我们的数据表明，这些mRNA的翻译受温度依赖性，uORF介导的调控。结论我们的数据表明，温度改变特定uORF的翻译可以调节酿酒酵母中的基因表达。我们的数据表明，这些mRNA的翻译受温度依赖性，uORF介导的调控。结论我们的数据表明，温度改变特定uORF的翻译可以调节酿酒酵母中的基因表达。