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Nascent 60S ribosomal subunits enter the free pool bound by Nmd3p

Published online by Cambridge University Press:  08 December 2000

JENNIFER HEI-NGAM HO
Affiliation:
Section of Molecular Genetics and Microbiology and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712-1095, USA
GEORGE KALLSTROM
Affiliation:
Section of Molecular Genetics and Microbiology and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712-1095, USA
ARLEN W. JOHNSON
Affiliation:
Section of Molecular Genetics and Microbiology and The Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas 78712-1095, USA
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Abstract

Nmd3p from yeast is required for the export of the large (60S) ribosomal subunit from the nucleus (Ho et al., 2000). Here, we show that Nmd3p forms a stable complex with free 60S subunits. Using an epitope-tagged Nmd3p, we show that free 60S subunits can be coimmunoprecipitated with Nmd3p. The interaction was specific for 60S subunits; 40S subunits were not coimmunoprecipitated. Using this coprecipitation technique and pulse-chase labeling of ribosomal subunit proteins we showed that Nmd3p bound nascent subunits, consistent with its role in export. However, under conditions in which ribosome biogenesis was inhibited (e.g., inhibition of transcription with thiolutin, inhibition of transcription of ribosomal protein and RNA genes in a sly1-1 mutant at nonpermissive temperature, and inhibition of translation in a conditional prt1 mutant), Nmd3p remained associated with 60S subunits. In addition, Nmd3Δ120, a truncated protein that lacked a nuclear localization signal, retained 60S binding. These results suggest that Nmd3p recruits nascent 60S subunits into the pool of free 60S subunits and exchanges on 60S subunits as they recycle during translation.

Type
Research Article
Copyright
2000 RNA Society

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