The function of RCC1/Ran complex.

RCC1基因被克隆为人类基因，以补充金仓鼠BHK21细胞系的温度敏感（ts）突变体tsBN2细胞；G1阻滞和限制性温度下有丝分裂的过早起始。它的同源物已从萌芽（SRM1/PRP20/MTR1）、裂变酵母（pim1）和果蝇（BJ1）以及仓鼠和爪蟾RCC1中分离出来。Bischoff和Ponstingle发现RCC1在核小G蛋白Ran/TC4上起GNRP（Duanine nucleotide releasing protein）的作用。根据G蛋白的模型，它从受体那里接收信号，一旦信号从细胞表面转导，就传递到下游。因此，一些与受体相对应的因子应该位于RCC1/Ran系统的上游。这种因子可能是DNA分子的想法非常有趣，而且显然是合理的，因为RCC1在染色体上的位置丰富；一个RCC1分子每1到10个核…更多一些。我们的模型如下。DNA分子的复制状态，如；它的起始，延伸和完成，将通过RCC1: Ran系统转移到下游，包括MPF的调节器，一个中央细胞周期引擎。基于这个模型，我们假设RCC1至少有两个结构域：与染色体结合或与Ran/TC4结合。这些结合结构域应该位于重复序列中，因为在重复序列外n端缺失的RCC1蛋白确实补足了tsBN2细胞。在RCC1中发现这样一个结构域将是阐明RCC1/Ran系统在细胞周期中的功能的关键一步。因此，我们根据丙氨酸扫描法制作了RCC1突变体。由于tsBN2细胞的内源性RCC1蛋白在39.5℃的温度下突变而消失，我们可以通过构建表达突变RCC1蛋白的tsBN2细胞转化子来研究突变RCC1蛋白在体内的功能。我们发现突变RCC1的GNRF活性与其补足tsBN2细胞的能力相关。少

The RCC1 gene was cloned as the human gene complementing tsBN2 cells, a temperature sensitive(ts)mutant of the BHK21 cell line derived from golden hamsters which show the cell cycle defect ; G1 arrest, and premature initiation of mitosi at the restrictive temperature. Its homologes have been isolated from both buddings (SRM1/PRP20/MTR1)and fission yeasts(pim1)and Drosophila(BJ1)in addition to hamster and Xenopus RCC1. Bischoff and Ponstingle have shown that RCC1 function as GNRP(Duanine nucleotide releasing protein)on the nuclear small G protein, Ran/TC4. According to the model of G protein, it pick up a signal from the receptor, in case of a signal transduction from the cell surface, and transfer to the downstream. Thus, some factors corresponding to the receptor should locate upstream of the RCC1/Ran system. The idea that such factor may be DNA molecule is very interesting and apparently reasonable, since RCC1 locates on chromosome abundantly ; one RCC1 molecule per one to ten nucleo … More somes. Our model is the following. The replication state of DNA molecule, such as ; its initiation, elongation and completion, will be transfer through the RCC1 : Ran system to the downstream, including a regulator of MPF, a central cell cycle engine. Based on this model, we suppose that the RCC1 has at least two domains : to bind with the chromosome or with Ran/TC4. These binding domains should locate in the repeat, since the RCC1 protein deleted in the N-terminal side outside of the repeat did complement tsBN2 cells. The identification of such a domain in the RCC1 will be a key step to clarify the function of the RCC1/Ran system on the cell cycle. Thus, we made the RCC1 mutants according to the alanine scanning method. Since in tsBN2 cells, endogeous RCC1 proteins disappear due to the mutation at 39.5ﾟC, we could investigate the functions of mutated RCC1, in vivo, by constructing transformants of tsBN2 cells expressing mutated RCC1 protein. We found that the GNRF activity of mutated RCC1 is correlated with its ability complimentating tsBN2 cells. Less