Hinnebusch A G
Proc Natl Acad Sci U S A. 1984 Oct;81(20):6442-6. doi: 10.1073/pnas.81.20.6442.
The GCN4 gene encodes a positive regulator of unlinked amino acid biosynthetic genes in yeast. I present evidence that the GCN4 gene is itself regulated by amino acid availability and that the regulation occurs at the translational level. A GCN4-lacZ fusion was used as a measure of the expression of GCN4 gene product. Starvation for histidine leads to derepression of the fusion enzyme in the wild type but not in a gcn2- strain. The gcn2- mutation does not reduce fusion transcript levels relative to wild type, suggesting that the product of GCN2 functions as an activator of GCN4 translation. The GCN4 transcript has a 5' leader that is approximately equal to 600 nucleotides long and contains four small open reading frames. A deletion of the small open reading frames results in constitutive derepression of fusion enzyme levels as the result of an approximately equal to 10-fold increase in the efficiency of translation of the fusion transcript. The deletion suppresses the requirement for GCN2 function. These results suggest that the GCN4 5' leader acts in cis to repress GCN4 translation and that GCN4 translation increases in response to amino acid starvation as the result of GCN2 antagonism of the repressing sequences in the GCN4 5' leader.
GCN4基因编码酵母中不相关氨基酸生物合成基因的一个正向调节因子。我提供的证据表明，GCN4基因本身受氨基酸可用性的调节，且这种调节发生在翻译水平。一个GCN4 - lacZ融合体被用作衡量GCN4基因产物表达的指标。组氨酸饥饿导致野生型中融合酶的去阻遏，但在gcn2 - 菌株中则不然。相对于野生型，gcn2 - 突变并不降低融合转录本水平，这表明GCN2的产物作为GCN4翻译的激活因子发挥作用。GCN4转录本有一个约600个核苷酸长的5'前导序列，并且包含四个小开放阅读框。小开放阅读框的缺失导致融合酶水平的组成型去阻遏，这是由于融合转录本翻译效率增加了约10倍所致。该缺失抑制了对GCN2功能的需求。这些结果表明，GCN4的5'前导序列以顺式作用抑制GCN4的翻译，并且由于GCN2对GCN4 5'前导序列中抑制序列的拮抗作用，GCN4的翻译在氨基酸饥饿时增加。
