Department of Cell Biology, The Lerner Research Institute, Cleveland Clinic, Cleveland, OH 44195, USA.
Cell. 2012 Mar 30;149(1):88-100. doi: 10.1016/j.cell.2012.02.018. Epub 2012 Mar 1.
Posttranscriptional regulatory mechanisms superimpose "fine-tuning" control upon "on-off" switches characteristic of gene transcription. We have exploited computational modeling with experimental validation to resolve an anomalous relationship between mRNA expression and protein synthesis. The GAIT (gamma-interferon-activated inhibitor of translation) complex repressed VEGF-A synthesis to a low, constant rate independent of VEGF-A mRNA expression levels. Dynamic model simulations predicted an inhibitory GAIT-element-interacting factor to account for this relationship and led to the identification of a truncated form of glutamyl-prolyl tRNA synthetase (EPRS), a GAIT constituent that mediates binding to target transcripts. The truncated protein, EPRS(N1), shields GAIT-element-bearing transcripts from the inhibitory GAIT complex, thereby dictating a "translational trickle" of GAIT target proteins. EPRS(N1) mRNA is generated by polyadenylation-directed conversion of a Tyr codon in the EPRS-coding sequence to a stop codon (PAY(∗)). Genome-wide analysis revealed multiple candidate PAY(∗) targets, including the authenticated target RRM1, suggesting a general mechanism for production of C terminus-truncated regulatory proteins.
转录后调控机制在基因转录的“开-关”开关特性之上叠加了“微调”控制。我们利用计算建模和实验验证来解决 mRNA 表达和蛋白质合成之间异常关系的问题。GAIT（γ-干扰素激活的翻译抑制剂）复合物将 VEGF-A 的合成抑制到一个低的、与 VEGF-A mRNA 表达水平无关的恒定速率。动态模型模拟预测了一种抑制性的 GAIT 元件相互作用因子来解释这种关系，并导致鉴定了一种谷氨酸-脯氨酸 tRNA 合成酶（EPRS）的截断形式，EPRS 是一种介导与靶转录本结合的 GAIT 成分。截断的蛋白质 EPRS（N1）将带有 GAIT 元件的转录本屏蔽在抑制性 GAIT 复合物之外，从而决定了 GAIT 靶蛋白的“翻译涓流”。EPRS（N1）mRNA 是通过聚腺苷酸化指导的 EPRS 编码序列中 Tyr 密码子向终止密码子（PAY(∗)）的转换产生的。全基因组分析显示了多个候选 PAY(∗) 靶标，包括已验证的靶标 RRM1，这表明产生 C 末端截断的调节蛋白的一般机制。
