High impact information on GAR1

• We isolated a RIO1 mutant in a screen for mutations synthetically lethal with a mutant allele of GAR1, an essential gene required for 18S rRNA production and rRNA pseudouridylation [1].
• These phenotypes are probably a direct consequence of the instability of H/ACA snoRNAs and Gar1p observed in cells deprived of Nhp2p or Nop10p [2].
• The nucleolar function of the other class of snoRNAs, which share box H and ACA elements and are associated with a glycine- and arginine-rich nucleolar protein, Gar1p, remains elusive [3].
• GAR1 is a non-ribosomal protein, localized in the yeast nucleolus, which is essential for cell growth [4].
• Indeed, depletion of Naf1p leads to a specific and dramatic decrease in the steady-state accumulation of all box H/ACA snoRNAs tested and of Cbf5p, Gar1p, and Nop10p [5].

Biological context of GAR1

• In Saccharomyces cerevisiae, the GAR1 gene is essential for cell viability [6].
• In this report, we have investigated the impact of arginine methylation on the Gar1, Nop1, and Nsr1 nucleolar proteins in Saccharomyces cerevisiae [7].
• A physical interaction between Gar1p and Rnt1pi is required for the nuclear import of H/ACA small nucleolar RNA-associated proteins [8].
• Using a bioinformatics approach, we also identified archaebacterial genes encoding candidate homologs of yeast Gar1p and Nop10p, two additional proteins known to be associated with eukaryotic box H/ACA snoRNPs [9].

Associations of GAR1 with chemical compounds

• snR31 is a RNA species of 225 nt. which has the trimethyl guanosine cap structure typical of small nuclear RNAs (snRNAs) and yeast small nucleolar RNAs (snoRNAs), and is associated with the nucleolar proteins fibrillarin (NOP1) and GAR1 [10].
• The 10-, 23-, and 25-kDa (GAR1) and 65-kDa proteins remain tightly associated with the snR30 RNA even after isopycnic sedimentation in cesium sulfate gradients [11].
• Genetic depletion of yeast Gar1p, an essential common component of H/ACA snoRNPs, leads to inhibition of uridine isomerizations to pseudo-uridines on the 35S pre-rRNA and of the early pre-rRNA cleavages at sites A1 and A2, resulting in a loss of mature 18S rRNA synthesis [12].
• Among the H/ACA snoRNAs associated with Gar1p, one can distinguish a large group of snoRNAs that are not essential in yeast and serve as guides for pseudouridine synthesis onto the pre-rRNA molecule [13].
• Glycerol gradient sedimentation and sequential immunoprecipitation experiments suggest that the Lsm protein-snR5 complex is partly distinct from the complex formed by snR5 RNA with the box H/ACA proteins Gar1p and Nhp2p [14].

Physical interactions of GAR1

• In vitro, Rnt1p binding to Gar1p is mutually exclusive of its RNA binding and cleavage activities [8].

Other interactions of GAR1

• Screens for mutations showing synthetic lethality with deletion of the SNR10 gene or with a temperature-sensitive gar1 allele both identified the ROK1 gene, encoding a putative, ATP-dependent RNA helicase of the DEAD-box family [15].
• Here we demonstrate the binding of a component of the H/ACA complex (Gar1p) to Rnt1p in vivo and in vitro in the absence of other factors [8].

Analytical, diagnostic and therapeutic context of GAR1

• Immunoprecipitation with anti-GAR1 antibodies shows that GAR1 is associated with a subset of snoRNAs, including snR10 and snR30 [4].
• To address this problem and further complete the snoRNA assignment to Psi sites, we identified the complete set of RNAs associated with the H/ACA snoRNP specific proteins Gar1p and Nhp2p by coupling TAP-tag purifications with genomic DNA microarrays experiments [16].
• By immunocytochemistry at the electron microscope level, we show that gar2 co-localizes with RNA polymerase I and the gar1 protein along the dense fibrillar component of the nucleolus in a wild-type strain of S. pombe, suggesting that gar2 is involved in the transcription and/or in the early steps of maturation of the ribosomal RNAs [17].

References