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The import of proteins into the nucleus is a process that involves at least 2 steps. The first is an energy-independent docking of the protein to the nuclear envelope and the second is an energy-dependent translocation through the nuclear pore complex. Imported proteins require a nuclear localization sequence (NLS) which generally consists of a short region of basic amino acids or 2 such regions spaced about 10 amino acids apart. Proteins involved in the first step of nuclear import have been identified in different systems. These include the Xenopus protein importin and its yeast homolog, SRP1 (a suppressor of certain temperature-sensitive mutations of RNA polymerase I in Saccharomyces cerevisiae), which bind to the NLS. KPNA2 protein interacts with the NLSs of DNA helicase Q1 and SV40 T antigen and may be involved in the nuclear transport of proteins. KPNA2 also may play a role in V(D)J recombination Characterization of an unusual importin alpha binding motif in the borna disease virus p10 protein that directs nuclear import. HPV16 E6 interacts with the karyopherin alpha2 adapter and can enter the nucleus of hela cells via a classical Kap alpha2beta1-mediated pathway. IPOA1 was localized at the lymphocyte plasma membrane. Its subcellular distribution was also studied. Identification of a karyopherin alpha 2 recognition site in PLAG1, which functions as a nuclear localization signal. 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. Results point to importin alpha1 as a critical downstream target of AMP-activated protein kinase (AMPK) and key mediator of AMPK-triggered HuR nuclear import. The model reflects experimentally determined rates for cargo import and correctly predicts that import is limited principally by Impalpha and Ran, but is also sensitive to NTF2. These observations indicate that importin-alpha functions as a mediator for the nuclear entry of Vpr. Confirmed the role of KPNA-2 in nuclear import of Chk2. Interaction with importin system is required for thioredoxin-binding protein-2 nuclear translocation and growth control tightly associated with TRX-dependent redox regulation of transcription factors.
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