title: Nuclear import and the evolution of a multifunctional RNA-binding protein.
abstract: La (SS-B) is a highly expressed protein that is able to bind 3'-oligouridylate and other common RNA sequence/structural motifs. By virtue of these interactions, La is present in a myriad of nuclear and cytoplasmic ribonucleoprotein complexes in vivo where it may function as an RNA-folding protein or RNA chaperone. We have recently characterized the nuclear import pathway of the S. cerevisiae La, Lhp1p. The soluble transport factor, or karyopherin, that mediates the import of Lhp1p is Kap108p/Sxm1p. We have now determined a 113-amino acid domain of Lhp1p that is brought to the nucleus by Kap108p. Unexpectedly, this domain does not coincide with the previously identified nuclear localization signal of human La. Furthermore, when expressed in Saccharomyces cerevisiae, the nuclear localization of Schizosaccharomyces pombe, Drosophila, and human La proteins are independent of Kap108p. We have been able to reconstitute the nuclear import of human La into permeabilized HeLa cells using the recombinant human factors karyopherin alpha2, karyopherin beta1, Ran, and p10. As such, the yeast and human La proteins are imported using different sequence motifs and dissimilar karyopherins. Our results are consistent with an intermingling of the nuclear import and evolution of La.
authors.affiliation: Laboratory of Cell Biology, Howard Hughes Medical Institute and Rockefeller University, New York, New York 10021, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Rosenblum
authors.forename: L F
authors.initials: LF
authors.lastname: Pemberton
authors.forename: N
authors.initials: N
authors.lastname: Bonifaci
authors.forename: G
authors.initials: G
authors.lastname: Blobel
mesh_terms: D001324:Autoantigens / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D019143:Evolution, Molecular; D005656:Fungal Proteins / Q000378:metabolism; D015966:Gene Expression Regulation, Fungal; D049452:Green Fluorescent Proteins; D006801:Humans; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D008969:Molecular Sequence Data; D019913:Nuclear Localization Signals / Q000502:physiology*; D009687:Nuclear Proteins / Q000378:metabolism; D010802:Phylogeny; D017434:Protein Structure, Tertiary; D012331:RNA, Fungal / Q000096:biosynthesis; D016601:RNA-Binding Proteins / Q000502:physiology*; D012261:Ribonucleoproteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D014157:Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D028901:alpha Karyopherins; D000097585:SS-B Antigen
chemical_list: D001324:Autoantigens; D005656:Fungal Proteins; D049452:Green Fluorescent Proteins; D007202:Indicators and Reagents; D008164:Luminescent Proteins; D019913:Nuclear Localization Signals; D009687:Nuclear Proteins; D012331:RNA, Fungal; D016601:RNA-Binding Proteins; D012261:Ribonucleoproteins; D014157:Transcription Factors; D028901:alpha Karyopherins; D000097585:SS-B Antigen