核质转运：一种热力学机制
Nucleocytoplasmic transport: a thermodynamic mechanism
摘要：
核孔支持真核细胞中细胞质和细胞核之间的分子通讯。蛋白质的选择性转运是由可溶性受体介导的，其通过小GTdR an的调节导致货物在核中积累或从核中消耗，即，核进口或核出口。我们认为这个运输系统的操作相结合的分析和实验方法。挑衅性的预测一个简单的模型进行了测试，使用无细胞核重建爪蟾卵提取物，一个系统非常适合于定量研究。我们发现，积累能力是有限的，因此，一种进口货物的引入会导致另一种货物的出口。显然，孔本身并不决定运输方向。此外，不同的货物达到一个类似的比例的核质浓度在稳态。该模型表明，这个比例实际上应该是独立的受体货物的亲和力，虽然动力学可能受到强烈的影响。数值守恒的系统组件之间的冲突突出的意见和流行的概念运输周期。我们认为，化学分区提供了一个框架，以了解通过平衡受体-货物中介产生浓度梯度的能力。
英文摘要：
The nuclear pore supports molecular communication between cytoplasm and nucleus in eukaryotic cells. Selective transport of proteins is mediated by soluble receptors, whose regulation by the small GTPase Ran leads to cargo accumulation in, or depletion from the nucleus, i.e., nuclear import or nuclear export. We consider the operation of this transport system by a combined analytical and experimental approach. Provocative predictions of a simple model were tested using cell-free nuclei reconstituted in Xenopus egg extract, a system well suited to quantitative studies. We found that accumulation capacity is limited, so that introduction of one import cargo leads to egress of another. Clearly, the pore per se does not determine transport directionality. Moreover, different cargo reach a similar ratio of nuclear to cytoplasmic concentration in steady-state. The model shows that this ratio should in fact be independent of the receptor-cargo affinity, though kinetics may be strongly influenced. Numerical conservation of the system components highlights a conflict between the observations and the popular concept of transport cycles. We suggest that chemical partitioning provides a framework to understand the capacity to generate concentration gradients by equilibration of the receptor-cargo intermediary.
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