Mechanism of the proteasome nuclear localization

26 S蛋白酶体是一种高度组织化的蛋白酶复合物，负责细胞溶质和核区室中的靶向蛋白质降解。在芽殖酵母和几种癌细胞中，已知26 S蛋白酶体主要位于细胞核中。虽然一些研究已经描述了核转位的机制，但仍不清楚蛋白酶体在组装过程中何时进入细胞核。利用双色荧光交叉相关光谱法（FCCS），我们测定了活酵母细胞中26 S蛋白酶体的局部浓度和动力学。令人惊讶的是，几乎所有的蛋白酶体亚基被纳入26 S蛋白酶体在细胞质和细胞核。重要的是，蛋白酶体动力学在输入中没有改变。（srp 1 -49）突变细胞，其中26 S蛋白酶体保留胞质溶胶。这些结果表明，26 S蛋白酶体在核转位之前在细胞质中完全组装。

The 26S proteasome is a highly organized protease complex that is responsible for targeted protein degradation in both the cytosolic and nuclear compartment. In budding yeast and several cancer cells, it is known that the 26S proteasome is mainly localized in the nucleus. Although several studies have described the mechanism of the nuclear translocation, it is still unclear when the proteasomes enter the nucleus upon their assembly process. Using dual color fluorescence cross correlation spectrometry(FCCS), we determined local concentration and dynamics of the 26S proteasome in living yeast cells. Surprisingly, almost all the proteasome subunits were incorporated into the 26S proteasome in both the cytosol and nucleus. Importantly, the proteasome dynamics was not changed in the importin.(srp1-49) mutant cells in which the 26S proteasome retains the cytosol. These results suggest that the 26S proteasome is fully assembled in the cytoplasm prior to the nuclear translocation.