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      Probing the nuclear import signal and nuclear transport molecular determinants of PRV ICP22


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          Herpes simplex virus 1 (HSV-1) ICP22 is a multifunctional protein and important for HSV-1 replication. Pseudorabies virus (PRV) ICP22 (P-ICP22) is a homologue of HSV-1 ICP22 and is reported to be able to selectively modify the transcription of different kinetic classes of PRV genes, however, the subcellular localization, localization signal and molecular determinants for its transport to execute this function is less well understood.


          In this study, by utilizing live cells fluorescent microscopy, P-ICP22 fused to enhanced yellow fluorescent protein (EYFP) gene was transient expressed in live cells and shown to exhibit a predominantly nucleus localization in the absence of other viral proteins. By transfection of a series of P-ICP22 deletion mutants fused to EYFP, a bona fide nuclear localization signal (NLS) and its key amino acids (aa) of P-ICP22 was, for the first time, determined and mapped to aa 41–60 (PASTPTPPKRGRYVVEHPEY) and aa 49–50 (KR), respectively. Besides, the P-ICP22 was demonstrated to be targeted to the nucleus via Ran-, importin α1-, and α7-mediated pathway.


          Our findings reported herein disclose the NLS and molecular mechanism for nuclear transport of P-ICP22, these results will uncover new avenues for depicting the biological roles of P-ICP22 during PRV infection.

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          Importin alpha: a multipurpose nuclear-transport receptor.

          The importin alpha/beta heterodimer targets hundreds of proteins to the nuclear-pore complex (NPC) and facilitates their translocation across the nuclear envelope. Importin alpha binds to classical nuclear localization signal (cNLS)-containing proteins and links them to importin beta, the karyopherin that ferries the ternary complex through the NPC. A second karyopherin, the exportin CAS, recycles importin alpha back to the cytoplasm. In this article, we discuss control mechanisms that importin alpha exerts over the assembly and disassembly of the ternary complex and we describe how new groups of importin alpha genes arose during the evolution of metazoan animals to function in development and differentiation. We also describe activities of importin alpha that seem to be distinct from its housekeeping functions in nuclear transport.
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            The GTP-binding protein Ran/TC4 is required for protein import into the nucleus.

            Two cytosolic fractions (A and B) from Xenopus oocytes are sufficient to support protein import into the nuclei of digitonin-permeabilized cells. Fraction A recognizes the nuclear localization sequence (NLS) and binds the import substrate to the nuclear envelope, whereas fraction B mediates the subsequent passage of the bound substrate into the nucleus. Here we report that two interacting components are required for full fraction-B activity, purify one of these components to homogeneity, and show that it is the highly abundant GTP-binding protein Ran (Ras-related nuclear protein)/TC4.
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              Nucleolar targeting: the hub of the matter.

              The nucleolus is a dynamic structure that has roles in various processes, from ribosome biogenesis to regulation of the cell cycle and the cellular stress response. Such functions are frequently mediated by the sequestration or release of nucleolar proteins. Our understanding of protein targeting to the nucleolus is much less complete than our knowledge of membrane-spanning translocation systems--such as those involved in nuclear targeting--and the experimental evidence reveals that few parallels exist with these better-characterized systems. Here, we discuss the current understanding of nucleolar targeting, explore the types of sequence that control the localization of a protein to the nucleolus, and speculate that certain subsets of nucleolar proteins might act as hub proteins that are able to bind to multiple protein targets. In parallel to other subnuclear structures, such as PML bodies, the proteins that are involved in the formation and maintenance of the nucleolus are inexorably linked to nucleolar trafficking.

                Author and article information

                +1186-20-37103316 , meili_2011@hotmail.com
                Cell Biosci
                Cell Biosci
                Cell & Bioscience
                BioMed Central (London )
                25 January 2016
                25 January 2016
                : 6
                : 3
                [ ]Department of Pathogenic Biology and Immunology, School of Basic Science, Guangzhou Medical University, Guangzhou, 511436 People’s Republic of China
                [ ]Guangzhou Hoffmann Institute of Immunology, School of Basic Science, Guangzhou Medical University, Guangzhou, 511436 People’s Republic of China
                [ ]Guangdong Haid Group Co., Ltd., Guangzhou, 511400 People’s Republic of China
                © Cai et al. 2016

                Open AccessThis article is distributed under the terms of the Creative Commons Attribution 4.0 International License ( http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver ( http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.

                : 4 August 2015
                : 10 January 2016
                Funded by: FundRef http://dx.doi.org/10.13039/501100001809, National Natural Science Foundation of China;
                Award ID: 31200120
                Award Recipient :
                Funded by: FundRef http://dx.doi.org/10.13039/501100001809, National Natural Science Foundation of China (CN);
                Award ID: 31400150
                Award Recipient :
                Funded by: Natural Science Foundation of Guangdong Province
                Award ID: S2013040016596
                Award ID: 2015A030313473
                Award Recipient :
                Funded by: Foundation for Distinguished Young Talents in Higher Education of Guangdong, China
                Award ID: 2013LYM_0096
                Award Recipient :
                Funded by: Pearl River S&T Nova Program of Guangzhou
                Award ID: 2013J2200018
                Award Recipient :
                Funded by: Science and Technology Program of Guangzhou, China
                Award ID: 201504291022514
                Award Recipient :
                Funded by: Scientific Research Projects in Colleges and universities of Guangzhou
                Award ID: 1201430024
                Award Recipient :
                Funded by: Scientific Research Foundation for the Ph.D., Guangzhou Medical University
                Award ID: 2014C02
                Award Recipient :
                Funded by: Medical Scientific Research Foundation of Guangdong Province, China
                Award ID: B2012165
                Award Recipient :
                Funded by: Training Program for Outstanding Young Teachers in Universities of Guangdong Province
                Funded by: Thousand Hundred Ten Projects of Guangzhou Medical University, Guangdong
                Funded by: Science and Technology Plan Projects of Guangdong Province, China
                Award ID: 2013B031800022
                Award Recipient :
                Funded by: Students’ extracurricular scientific and technological activities in Guangzhou Medical University
                Award ID: 2015A003
                Award ID: 2015A008
                Award ID: 2015A019
                Award ID: 2015B020
                Award Recipient :
                Custom metadata
                © The Author(s) 2016

                Cell biology
                prv icp22,nuclear transport,nuclear localization signal (nls),importin,ran-gtp
                Cell biology
                prv icp22, nuclear transport, nuclear localization signal (nls), importin, ran-gtp


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