Lehmann Andrea, Janek Katharina, Braun Beate, Kloetzel Peter-Michael, Enenkel Cordula
Institut für Biochemie, Humboldt Universität zu Berlin, Universitätsklinikum Charité, Monbijoustr. 2, Berlin, D-10117, Germany.
J Mol Biol. 2002 Mar 29;317(3):401-13. doi: 10.1006/jmbi.2002.5443.
The mechanism by which yeast 20 S proteasomes are imported into the nucleus is still unresolved. Here, we provide the first evidence that 20 S proteasomes are imported as precursor complexes into the nucleus. By using the srp1-49 mutant which is deficient in nuclear import of cargos with classical nuclear localization sequences (cNLS), we show that proteasome precursor complexes associate with importin/karyopherin alphabeta, the cNLS receptor, and that they accumulate inside the cytoplasm. Reconstitution assays revealed that only precursor complexes are targeted to the nuclear envelope (NE) by karyopherin alphabeta. In support, the green fluorescent protein (GFP)-labelled maturation factor Ump1, marking precursor complexes, mainly localizes to the nucleus and around the NE. Our data suggest that nuclear 20 S proteasomes are finally matured inside the nucleus.
酵母20 S蛋白酶体导入细胞核的机制仍未明确。在此，我们首次提供证据表明，20 S蛋白酶体以前体复合物的形式被导入细胞核。通过使用srp1 - 49突变体（该突变体缺乏对具有经典核定位序列（cNLS）的货物进行核输入的能力），我们发现蛋白酶体前体复合物与输入蛋白/核转运蛋白αβ（cNLS受体）结合，并在细胞质中积累。重组实验表明，只有前体复合物能被核转运蛋白αβ靶向至核膜（NE）。此外，绿色荧光蛋白（GFP）标记的成熟因子Ump1（标记前体复合物）主要定位于细胞核及核膜周围。我们的数据表明，细胞核中的20 S蛋白酶体最终在细胞核内成熟。
