Elevation of protein synthesis is a complex response to fertilisation
Elevation of protein synthesis is a complex response to fertilisation
复制标题
蛋白质合成的提高是对受精的复杂反应
作者：
J. Brandis;R. Raff
海胆未受精卵中的蛋白质合成速度较低。然而，受精会引发一系列反应，首先是精子进入后几秒钟内细胞内阳离子浓度的变化，然后延伸到一系列更复杂的事件1。由于这些事件在时间上是连续的，每个事件都可能依赖于前一个事件，或者可能存在一系列并行的独立路径。 Epel 等人证明后一种假设是正确的2，他们证明氨的人工激活未能引发钠流入和皮质反应等事件，但确实引发了多种其他事件，包括钾电导、蛋白质合成、DNA 合成和 mRNA 多腺苷酸化。我们一直在详细研究蛋白质合成的提高。在卵裂早期3，蛋白质合成速率增加数倍，最终达到比成熟卵母细胞高100倍的绝对速率4。 Kaumeyer 等人 5 和 Jenkins 等人 6 已经证明，未受精的鸡蛋含有“掩蔽”信使核糖核蛋白颗粒，除非经过修饰或去蛋白，否则这些颗粒在体外不可翻译。受精后蛋白质合成率的增加大部分是由于由于暴露7而募集了这种卵子发生mRNA。然而，这一增长的很大一部分也是由于翻译效率的提高8。根据 Palmiter9 的定义，翻译效率是每单位时间每条消息释放的完整多肽的数量。海胆卵受精后效率的变化反映在核糖体运动速率的增加（即受精后完成平均大小蛋白质所需的时间减少）以及随之而来的起始速率的增加。可用于翻译的 mRNA 数量的增加和翻译效率的提高对蛋白质合成的净影响是倍增的。我们在这里提供的证据表明这两个过程处于单独的控制之下。
PROTEIN SYNTHESIS in unfertilised eggs of the sea urchin proceeds at a low rate. However, fertilisation triggers a series of reactions beginning with changes in intracellular cation concentrations within a few seconds of sperm entry and extending to a cascade of more complex events1. As these events are sequential in time, each might depend on the preceding event, or there might be a parallel series of independent pathways. The latter hypothesis was shown to be correct by Epel et al.2, who demonstrated that artificial activation with ammonia failed to initiate events such as sodium influx and the cortical reactions but did initiate a variety of others including potassium conductance, protein synthesis, DNA synthesis and mRNA polyadenylation. We have been studying the elevation of protein synthesis in detail. The rate of protein synthesis increases severalfold during the early cleavage stages3 and eventually reaches an absolute rate which is 100 times higher than that in the mature oocyte4. Kaumeyer et al.5 and Jenkins et al.6 have demonstrated that unfertilised eggs contain ‘masked’ messenger ribonucleoprotein particles which are not translatable in vitro unless modified or deproteinised. Most of the increase in the rate of protein synthesis following fertilisation is due to the recruitment of this oogenetic mRNA as a result of unmasking7. However, a significant portion of the rise also results from an increase in translational efficiency8. As defined by Palmiter9, translational efficiency is the number of completed polypeptides released per unit time per message. The change in efficiency following fertilisation of sea urchin eggs is reflected in an increase in the rate of ribosome movement (that is, the time required to complete an average size protein decreases after fertilisation) coupled to a concomitant increase in initiation rate. The net effect on protein synthesis of an increase in number of mRNAs available for translation and an increase in translational efficiency is multiplicative. We present evidence here that these two processes are under separate controls.