Loc1p is required for efficient assembly and nuclear export of the 60S ribosomal subunit.
Loc1p is an exclusively nuclear dsRNA-binding protein that affects the asymmetric sorting of ASH1 mRNA to daughter cells in Saccharomyces cerevisiae. In addition to the role in cytoplasmic RNA localization, Loc1p is a constituent of pre-60S ribosomes. Cells devoid of Loc1p display a defect in the synthesis of 60S ribosomal subunits, resulting in "half-mer" polyribosomes. Previously, we reported that Loc1p is located throughout the entire nucleus; however, upon closer inspection we discovered that Loc1p is enriched in the nucleolus consistent with a role in 60S ribosome biogenesis. Given that Loc1p is an RNA-binding protein and presumably functions in the assembly of 60S ribosomal subunits, we investigated if Loc1p has a role in rRNA processing and nuclear export of 60S subunits. Analysis of pre-rRNA processing revealed that loc1Delta cells exhibit gross defects in 25S rRNA synthesis, specifically a delay in processing at sites A0, A1 and A2 in 35S pre-rRNA. Furthermore, loc1Delta cells exhibit nuclear export defects for 60S ribosomal subunits, again, consistent with a role for Loc1p in the assembly of 60S ribosomal subunits. It is attractive to hypothesize that the two phenotypes associated with loc1Delta cells, namely altered ASH1 mRNA localization and ribosome biogenesis, are not mutually exclusive, but that ribosome biogenesis directly impacts mRNA localization.
Urbinati
Carl R
CR
Department of Microbiology and Molecular Genetics, Medical College of Wisconsin, 8701 Watertown Plank Road, Milwaukee, WI 53226, USA.
Gonsalvez
Graydon B
GB
Aris
John P
JP
Long
Roy M
RM
D021581:Active Transport, Cell Nucleus; D001483:Base Sequence; D004271:DNA, Fungal / Q000235:genetics; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D012322:RNA Precursors / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional; D012331:RNA, Fungal / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D012097:Repressor Proteins / Q000235:genetics / Q000378:metabolism; D012270:Ribosomes / Q000737:chemistry / Q000378:metabolism*; D012441:Saccharomyces cerevisiae / Q000235:genetics / Q000378:metabolism; D029701:Saccharomyces cerevisiae Proteins / Q000235:genetics / Q000378:metabolism*
C098733:ASH1 protein, S cerevisiae; D004271:DNA, Fungal; D004268:DNA-Binding Proteins; C426224:LOC1 protein, S cerevisiae; D009687:Nuclear Proteins; D012322:RNA Precursors; D012331:RNA, Fungal; D016601:RNA-Binding Proteins; D012097:Repressor Proteins; D029701:Saccharomyces cerevisiae Proteins