title: Expression, cellular localization, and enzymatic activities of RNA helicase II/Gu(beta).
abstract: RNA helicase II/Gu (RH-II/Gu) is a nucleolar DEAD-box protein that unwinds double-stranded RNA and introduces secondary structure to a single-stranded RNA. We recently identified its paralogue, RH-II/Gu(beta), in contrast to the original RH-II/Gu(alpha). Their similar intron-exon structures on chromosome 10 suggest gene duplication. To determine functional differences, their expression, localization, and enzymatic activities were compared. RH-II/Gu(alpha) is expressed two- to threefold more than RH-II/Gu(beta) in most tissues. Both proteins localize to nucleoli, suggesting roles in ribosomal RNA production, but RH-II/Gu(beta) also localizes to nuclear speckles containing splicing factor SC35, suggesting possible involvement in pre-mRNA splicing. The C-terminus responsible for nuclear speckle localization of RH-II/Gu(beta) contains an arginine-serine-rich domain present in some RNA splicing proteins. In vitro assays show weaker ATPase and RNA helicase activities of RH-II/Gu(beta). RH-II/Gu(alpha) unwinds RNA substrate with a 21- or 34-nt duplex and 5' overhangs, but RH-II/Gu(beta) unwinds only the shorter duplex. Although RH-II/Gu(beta) has no RNA folding activity, it catalyzes formation of an RNA complex with unidentified structure, which is not observed when assayed with a mixture of the two enzymes. Instead, the presence of RH-II/Gu(beta) stimulates RH-II/Gu(alpha) unwinding activity. Our data suggest distinct and complex regulation of expression of the two paralogues with nonredundant gene products.
authors.affiliation: Department of Pharmacology, Baylor College of Medicine, One Baylor Plaza, Houston, Texas 77030, USA. bvaldez@bcm.tmc.edu
authors.forename: Benigno C
authors.initials: BC
authors.lastname: Valdez
authors.forename: Laszlo
authors.initials: L
authors.lastname: Perlaky
authors.forename: Dale
authors.initials: D
authors.lastname: Henning
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000187:drug effects / Q000235:genetics; D000595:Amino Acid Sequence; D000818:Animals; D002451:Cell Compartmentation / Q000235:genetics*; D002466:Cell Nucleolus / Q000201:enzymology / Q000235:genetics; D002467:Cell Nucleus / Q000201:enzymology*; D002478:Cells, Cultured; D053487:DEAD-box RNA Helicases; D003609:Dactinomycin / Q000494:pharmacology; D005057:Eukaryotic Cells / Q000201:enzymology*; D015971:Gene Expression Regulation, Enzymologic / Q000235:genetics*; D015972:Gene Expression Regulation, Neoplastic / Q000235:genetics; D006801:Humans; D007527:Isoenzymes / Q000235:genetics / Q000378:metabolism; D008969:Molecular Sequence Data; D015530:Nuclear Matrix / Q000201:enzymology / Q000235:genetics; D019384:Nucleic Acid Synthesis Inhibitors / Q000494:pharmacology; D020365:RNA Helicases / Q000235:genetics* / Q000378:metabolism*; D012326:RNA Splicing / Q000235:genetics; D012330:RNA, Double-Stranded / Q000187:drug effects / Q000235:genetics / Q000378:metabolism; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D012335:RNA, Ribosomal / Q000235:genetics*; D014407:Tumor Cells, Cultured / Q000201:enzymology
chemical_list: D007527:Isoenzymes; D019384:Nucleic Acid Synthesis Inhibitors; D012330:RNA, Double-Stranded; D012333:RNA, Messenger; D012335:RNA, Ribosomal; D003609:Dactinomycin; C448980:DDX50 protein, human; D053487:DEAD-box RNA Helicases; D020365:RNA Helicases