title: Importin alpha/beta-mediated nuclear protein import is regulated in a cell cycle-dependent manner.
abstract: Functional nuclear proteins are selectively imported into the nucleus by transport factors such as importins alpha and beta. The relationship between the efficiency of nuclear protein import and the cell cycle was measured using specific import substrates for the importin alpha/beta-mediated pathway. After the microinjection of SV40 T antigen nuclear localization signal (NLS)-containing substrates into the cytoplasm of synchronized culture cells at a certain phase of the cell cycle, the nuclear import of the substrates was measured kinetically. Cell cycle-dependent change in import efficiency, but not capacity, was found. That is, import efficiency was found low in the early S, G2/M, and M/G1 phases compared with other phases. In addition, we found that the extent of co-imunoprecipitation of importin alpha with importin beta from cell extracts was strongly associated with import efficiency. These results indicate that the importin alpha/beta-mediated nuclear import machinery is regulated in a cell cycle-dependent manner through the modulation of interaction modes between importins alpha and beta.
authors.affiliation: Department of Frontier Biosciences, Graduate School of Frontier Biosciences, Osaka University, 2-2 Yamada-oka, Suita, Osaka 565-0871, Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Yasuhara
authors.forename: Eri
authors.initials: E
authors.lastname: Takeda
authors.forename: Hitomi
authors.initials: H
authors.lastname: Inoue
authors.forename: Ippei
authors.initials: I
authors.lastname: Kotera
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Yoneda
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology; D000952:Antigens, Polyomavirus Transforming / Q000378:metabolism / Q000494:pharmacology; D002451:Cell Compartmentation / Q000235:genetics; D002453:Cell Cycle / Q000502:physiology*; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism*; D016195:G2 Phase / Q000235:genetics; D006367:HeLa Cells; D006801:Humans; D007700:Kinetics; D008938:Mitosis / Q000235:genetics; D021381:Protein Transport / Q000502:physiology; D016196:S Phase / Q000235:genetics; D015398:Signal Transduction / Q000235:genetics; D028901:alpha Karyopherins / Q000235:genetics / Q000378:metabolism*; D028961:beta Karyopherins / Q000235:genetics / Q000378:metabolism*
chemical_list: D000952:Antigens, Polyomavirus Transforming; D028901:alpha Karyopherins; D028961:beta Karyopherins; C087978:karyopherin alpha 2