title: The quantitative assessment of the role played by basic amino acid clusters in the nuclear uptake of human ribosomal protein L7.
abstract: In this study, we used a multiple copy (EGFP)(3) reporter system to establish a numeric nuclear index system to assess the degree of nuclear import. The system was first validated by a FRAP assay, and then was applied to evaluate the essential and multifaceted nature of basic amino acid clusters during the nuclear import of ribosomal protein L7. The results indicate that the sequence context of the basic cluster determines the degree of nuclear import, and that the number of basic residues in the cluster is irrelevant; rather the position of the pertinent basic residues is crucial. Moreover, it also found that the type of carrier protein used by basic cluster has a great impact on the degree of nuclear import. In case of L7, importin β2 or importin β3 are preferentially used by clusters with a high import efficiency, notwithstanding that other importins are also used by clusters with a weaker level of nuclear import. Such a preferential usage of multiple basic clusters and importins to gain nuclear entry would seem to be a common practice among ribosomal proteins in order to ensure their full participation in high rate ribosome synthesis.
authors.affiliation: Institute of Genome Sciences, National Yang-Ming University, Taipei, Taiwan, ROC.
authors.forename: Lin-Ru
authors.initials: LR
authors.lastname: Tai
authors.forename: Chang-Wei
authors.initials: CW
authors.lastname: Chou
authors.forename: I-Fang
authors.initials: IF
authors.lastname: Lee
authors.forename: Ralph
authors.initials: R
authors.lastname: Kirby
authors.forename: Alan
authors.initials: A
authors.lastname: Lin
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000235:genetics; D000595:Amino Acid Sequence; D024361:Amino Acids, Basic / Q000502:physiology*; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D036681:Fluorescence Recovery After Photobleaching; D049452:Green Fluorescent Proteins / Q000032:analysis / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D021381:Protein Transport / Q000187:drug effects / Q000235:genetics; D034741:RNA, Small Interfering / Q000494:pharmacology; D012269:Ribosomal Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D014162:Transfection; D028961:beta Karyopherins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism / Q000502:physiology
chemical_list: D024361:Amino Acids, Basic; C107940:IPO5 protein, human; D034741:RNA, Small Interfering; C053634:RPL7 protein, human; D012269:Ribosomal Proteins; C108121:TNPO1 protein, human; D028961:beta Karyopherins; C485184:enhanced green fluorescent protein; D049452:Green Fluorescent Proteins