gar2 is a nucleolar protein fromSchizosaccharomyces pomberequired for 18S rRNA and 40S ribosomal subunit accumulation

Abstract

Several nucleolar proteins, such as nucleolin, NOP1/fibrillarin, SSB1, NSR1 and GAR1 share a common glycine and arginine rich structural motif called the GAR domain. To identify novel nucleolar proteins from fission yeast we screened Schizosaccharomyces pombe genomic DNA libraries with a probe encompassing the GAR structural motif. Here we report the identification and characterization of a S.pombe gene coding for a novel nucleolar protein, designated gar2. The structure of the fission yeast gar2 is reminiscent of that of nucleolin from vertebrates and NSR1 from Saccharomyces cerevisiae. In addition, like these proteins, gar2 has a nucleolar localisation. The disruption of the gar2+ gene affects normal cell growth, leads to an accumulation of 35S pre-rRNA and a decrease of mature 18S rRNA steady state levels. Moreover, ribosomal profiles of the mutant show an increase of free 60S ribosomal subunits and an absence of free 40S ribosomal subunits. gar2 is able to rescue a S.cerevisiae mutant lacking NSR1, thus establishing gar2 as a functional homolog of NSR1. We propose that gar2 helps the assembly of pre-ribosomal particles containing 18S rRNA.

Nucleolin inhibits Hdm2 by multiple pathways leading to p53 stabilization

“…This may simply be a consequence of the critical role that nucleolin plays in rRNA maturation. Budding and fission yeasts deleted for the gene encoding a nucleolin homolog (NSR1 and gar2 þ , respectively) are viable, but show severe growth defects and have aberrant pre-rRNA processing (Kondo and Inouye, 1992;Lee et al, 1992;Gulli et al, 1995). Similarly, our RNAi-mediated downmodulation of nucleolin causes toxic effects on cell viability (data not shown), likely resulting from an inability to properly process rRNA.…”

“…In response to c-Myc or a heightened cellular proliferation rate, nucleolin levels can increase B4-fold (Sirri et al, 1997;Greasley et al, 2000). Nucleolin functions at an early step in precursor ribosomal RNA (rRNA) processing (Ginisty et al, 1998;Borovjagin and Gerbi, 2004), and disruption of nucleolin homologs in yeast cause unbalanced production of the large and small ribosome subunits (Kondo and Inouye, 1992;Lee et al, 1992;Gulli et al, 1995). Although the yeast strains lacking expression of the homologs are viable, they show severe defects in growth, strongly suggesting that knockouts (ko) of the mammalian protein will be lethal.…”

The GTP-binding protein YqeH participates in biogenesis of the 30S ribosome subunit in Bacillus subtilis

“…Thus, depletion of YqeH appears to result in both retardation of 30S assembly and destabilization of the premature 30S subunit. During biogenesis of the 30S subunit, pre-16S rRNA interacts with ribosomal proteins and non-ribosomal factors to form pre-ribosomal intermediates (Gulli et al, 1995). In YqeH-depleted cells, a proportion of the newly synthesized 30S intermediates may be impaired, thus rendering the pre-16S rRNA more susceptible to RNase degradation.…”

Characterization of AtNUC-L1 Reveals a Central Role of Nucleolin in Nucleolus Organization and Silencing of AtNUC-L2 Gene in Arabidopsis

“…Mutations of genes encoding nucleolin homologue in budding (NSR1) and fission (GAR2) yeast produce severe effects on cell growth and disrupt balanced production of the small and large ribosomal subunits (Lee et al, 1992;Gulli et al, 1995). Moreover, it has been shown that the nucleolar structure in gar2 cells is dramatically reorganized and unusual structures are detected (Leger-Silvestre et al, 1997).…”