GAR1 is an essential small nucleolar RNP protein required for pre-rRNA processing in yeast.

Abstract

Among the few proteins of the eukaryotic nucleolus that have been characterized, four proteins, nucleolin, fibrillarin, SSB1 and NSR1, possess a common structural motif, the GAR domain, which is rich in glycine and arginine residues. In order to examine whether the presence of this domain is characteristic of a family of nucleolar proteins, we investigated whether other yeast genes encode proteins containing GAR domains. We report here the sequence and the characterization of a new yeast gene, GAR1, which encodes a protein of 205 residues containing two GAR domains. GAR1 is a non‐ribosomal protein, localized in the yeast nucleolus, which is essential for cell growth. Immunoprecipitation with anti‐GAR1 antibodies shows that GAR1 is associated with a subset of snoRNAs, including snR10 and snR30. Depletion of GAR1 by expression under the control of a regulated GAL promoter, impairs processing of the 35S primary transcript of pre‐rRNA and prevents synthesis of 18S rRNA. GAR1 is thus the fifth member of a family of nucleolar proteins containing GAR domains, and is involved in rRNA metabolism.

Telomerase in the human organism

“…These proteins were ®rst identi®ed in budding yeast as Gar1p, Cbf5p, Nhp2p and Nop10p (Girard et al, 1992;Balakin et al, 1996;Ganot et al, 1997;Lafontaine et al, 1998;Watkins et al, 1998;Henras et al, 1998). Loss of expression of any one of these proteins results in growth arrest with aberrant rRNA, and loss of any one except Gar1p prevents the accumulation of H/ACA snoRNAs.…”

The family of box ACA small nucleolar RNAs is defined by an evolutionarily conserved secondary structure and ubiquitous sequence elements essential for RNA accumulation.

“…The derived amino acid sequence of the GARl-ProtA fusion protein around the fusion sites was GARl amino-terminal residues (Met-l-Gly-5), linker sequence (Asp-Pro-Arg-PheGly), GARl (Gly-6-Arg-205), two IgG-binding units, and linker sequence (Asp-Pro-Asn-Leu-Ala-Arg-Lys-Lys). The GALr.garl yeast strain (Girard et al 1992) was transformed with pMC GZZl. Following transfer to glucose medium, the transformant yeast cells showed no deviation in growth rate in comparison to the wild-type strain, demonstrating that the plasmid-encoded GARl-ProtA fusion protein is able to complement the other wise lethal gar' mutant.…”

“…Fibrillarin has been suggested to be common to all yeast snoRNPs, with the exception of 7-2/MRP. The GARl protein, an essential glycine/arginine-rich nucleolar protein (Girard et al 1992), seems to be specific to the ACA box-con taining snoRNAs (Balakin et al 1996). Two yeast ACA snoRNAs, snRlO and snRll, are precipitable with anti bodies directed against another nucleolar protein, SSBl (Clark et al 1990).…”

The 18S rRNA dimethylase Dim1p is required for pre-ribosomal RNA processing in yeast.

“…Genetic depletion of the RNA or protein components of the U3, U14, snR10, or snR3O small nucleolar ribonucleoproteins (snoRNPs) also inhibits processing at sites A1 and A2, preventing synthesis of the mature 18s rRNA (Tollervey 1987;Li et al 1990; Hughes and Ares 1991; Tollervey et al 1991;Girard et al 1992;Monissey and Tollervey 1993). The pattern of processing observed in these mutants is, however, different from that seen in the Dimlp-depleted strain; no accumulation of the 33s or 22s pre-rRNAs is obsenred, instead the snoRNP mutants accumulate a 23s prerRNA that extends from the 5' end of the 35s pre-rRNA to site A3 and is generated by direct cleavage of the 35s pre-rRNA at A3 ).…”