title: Genetic analysis of the ribosome biogenesis factor Ltv1 of Saccharomyces cerevisiae.
abstract: Ribosome biogenesis has been studied extensively in the yeast Saccharomyces cerevisiae. Yeast Ltv1 is a conserved 40S-associated biogenesis factor that has been proposed to function in small subunit nuclear export. Here we show that Ltv1 has a canonical leucine-rich nuclear export signal (NES) at its extreme C terminus that is both necessary for Crm1 interaction and Ltv1 export. The C terminus of Ltv1 can substitute for the NES in the 60S-export adapter Nmd3, demonstrating that it is a functional NES. Overexpression of an Ltv1 lacking its NES (Ltv1∆C13) was strongly dominant negative and resulted in the nuclear accumulation of RpS3-GFP; however, export of the pre-40S was not affected. In addition, expression of endogenous levels of Ltv1∆C protein complemented both the slow-growth phenotype and the 40S biogenesis defect of an ltv1 deletion mutant. Thus, if Ltv1 is a nuclear export adapter for the pre-40S subunit, its function must be fully redundant with additional export factors. The dominant negative phenotype of Ltv1∆NES overexpression was suppressed by co-overexpressing RpS3 and its chaperone, Yar1, or by deletion of the RpS3-binding site in Ltv1∆NES, suggesting that titration of RpS3 by Ltv1∆NES is deleterious in yeast. The dominant-negative phenotype did not correlate with a decrease in 40S levels but rather with a reduction in the polysome-to-monosome ratio, indicating reduced rates of translation. We suggest that titration of RpS3 by excess nuclear Ltv1 interferes with 40S function or with a nonribosomal function of RpS3.
authors.affiliation: Biochemistry and Molecular Biology Program, Lewis & Clark College, Portland, Oregon 97219.
authors.forename: Jason R
authors.initials: JR
authors.lastname: Merwin
authors.affiliation: Biochemistry and Molecular Biology Program, Lewis & Clark College, Portland, Oregon 97219.
authors.forename: Lucien B
authors.initials: LB
authors.lastname: Bogar
authors.affiliation: Biochemistry and Molecular Biology Program, Lewis & Clark College, Portland, Oregon 97219.
authors.forename: Sarah B
authors.initials: SB
authors.lastname: Poggi
authors.affiliation: Biochemistry and Molecular Biology Program, Lewis & Clark College, Portland, Oregon 97219.
authors.forename: Rebecca M
authors.initials: RM
authors.lastname: Fitch
authors.affiliation: Department of Molecular Biosciences, University of Texas, Austin, Texas 78712.
authors.forename: Arlen W
authors.initials: AW
authors.lastname: Johnson
authors.affiliation: Biochemistry and Molecular Biology Program, Lewis & Clark College, Portland, Oregon 97219 lycan@lclark.edu.
authors.forename: Deborah E
authors.initials: DE
authors.lastname: Lycan
mesh_terms: D021581:Active Transport, Cell Nucleus; D000595:Amino Acid Sequence; D001665:Binding Sites; D002467:Cell Nucleus / Q000378:metabolism; D016384:Consensus Sequence; D005799:Genes, Dominant; D005816:Genetic Complementation Test; D049452:Green Fluorescent Proteins / Q000378:metabolism; D047468:Immunoprecipitation; D028884:Karyopherins / Q000378:metabolism; D008969:Molecular Sequence Data; D009154:Mutation / Q000235:genetics; D049790:Nuclear Export Signals; D010641:Phenotype; D011485:Protein Binding; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D012269:Ribosomal Proteins / Q000378:metabolism; D012270:Ribosomes / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics* / Q000254:growth & development; D029701:Saccharomyces cerevisiae Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D013329:Structure-Activity Relationship; D000097606:Exportin 1 Protein
chemical_list: D049452:Green Fluorescent Proteins; D028884:Karyopherins; D049790:Nuclear Export Signals; D018160:Receptors, Cytoplasmic and Nuclear; D011993:Recombinant Fusion Proteins; D012269:Ribosomal Proteins; D029701:Saccharomyces cerevisiae Proteins; D000097606:Exportin 1 Protein; C501335:LTV1 protein, S cerevisiae; C044152:ribosomal protein S3
keywords: Ltv1; RpS3; nuclear export; ribosome biogenesis; small subunit