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The SpGAR1 gene of Schizosaccharomyces pombe encodes the functional homologue of the snoRNP protein GAR1 of Saccharomyces cerevisiae.

ABSTRACT: GAR1 is a nucleolar protein which is associated with small nucleolar RNAs (snoRNAs) and which is required for pre-ribosomal RNA processing. In Saccharomyces cerevisiae, the GAR1 gene is essential for cell viability. We have cloned and sequenced the GAR1 gene from the distantly related yeast Schizosaccharomyces pombe. The SpGAR1 gene, which contains two small introns, codes for a 194 amino-acid protein of 20 kDa. A protein sequence comparison indicates that SpGAR1 is 65% identical to ScGAR1. Anti-ScGAR1 antibodies recognize SpGAR1, emphasizing the structural conservation of the protein. Immunostaining of S.pombe cells with these antibodies reveals that SpGAR1 is localized in the nucleolus, as is the case in S.cerevisiae. Moreover, SpGAR1 can substitute for GAR1 in S.cerevisiae, indicating that the two proteins are functionally equivalent. These results suggest a parallel evolutionary conservation of proteins and RNAs with which GAR1 interacts in mediating its pre-rRNA processing and viability functions. After fibrillarin, GAR1 is the second protein of the snoRNPs shown to have been conserved throughout evolution.

SUBMITTER: Girard JP

PROVIDER: S-EPMC309478 | biostudies-other | 1993 May

REPOSITORIES: biostudies-other

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The SpGAR1 gene of Schizosaccharomyces pombe encodes the functional homologue of the snoRNP protein GAR1 of Saccharomyces cerevisiae.

Girard J P JP Caizergues-Ferrer M M Lapeyre B B

Nucleic acids research 19930501 9

GAR1 is a nucleolar protein which is associated with small nucleolar RNAs (snoRNAs) and which is required for pre-ribosomal RNA processing. In Saccharomyces cerevisiae, the GAR1 gene is essential for cell viability. We have cloned and sequenced the GAR1 gene from the distantly related yeast Schizosaccharomyces pombe. The SpGAR1 gene, which contains two small introns, codes for a 194 amino-acid protein of 20 kDa. A protein sequence comparison indicates that SpGAR1 is 65% identical to ScGAR1. Anti ...[more]

PMID: 8502556

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Project description:The Schizosaccharomyces pombe spo20-KC104 mutation was originally isolated in a screen for sporulation-deficient mutants, and the spo20-KC104 mutant exhibits temperature-sensitive growth. Herein, we report that S. pombe, spo20(+) is essential for fission yeast cell viability and is constitutively expressed throughout the life cycle. We also demonstrate that the spo20(+) gene product is structurally homologous to Saccharomyces cerevisiae Sec14, the major phosphatidylinositol transfer protein of budding yeast. This structural homology translates to a significant degree of functional relatedness because reciprocal complementation experiments demonstrate that each protein is able to fulfill the essential function of the other. Moreover, biochemical experiments show that, like Sec14, Spo20 is a phosphatidylinositol/phosphatidylcholine-transfer protein. That Spo20 is required for Golgi secretory function in vegetative cells is indicated by our demonstration that the spo20-KC104 mutant accumulates aberrant Golgi cisternae at restrictive temperatures. However, a second phenotype observed in Spo20-deficient fission yeast is arrest of cell division before completion of cell separation. Consistent with a direct role for Spo20 in controlling cell septation in vegetatively growing cells, localization experiments reveal that Spo20 preferentially localizes to the cell poles and to sites of septation of fission yeast cells. We also report that, when fission yeasts are challenged with nitrogen starvation, Spo20 translocates to the nucleus. This nuclear localization persists during conjugation and meiosis. On completion of meiosis, Spo20 translocates to forespore membranes, and it is the assembly of forespore membranes that is abnormal in spo20-KC104 cells. In such mutants, a considerable fraction of forming prespores fail to encapsulate the haploid nucleus. Our results indicate that Spo20 regulates the formation of specialized membrane structures in addition to its recognized role in regulating Golgi secretory function.

Project description:BackgroundMicrosporidia, parasitic fungi-related eukaryotes infecting many cell types in a wide range of animals (including humans), represent a serious health threat in immunocompromised patients. The 2.9 Mb genome of the microsporidium Encephalitozoon cuniculi is the smallest known of any eukaryote. Eukaryotic protein kinases are a large superfamily of enzymes with crucial roles in most cellular processes, and therefore represent potential drug targets. We report here an exhaustive analysis of the E. cuniculi genomic database aimed at identifying and classifying all protein kinases of this organism with reference to the kinomes of two highly-divergent yeast species, Saccharomyces cerevisiae and Schizosaccharomyces pombe.ResultsA database search with a multi-level protein kinase family hidden Markov model library led to the identification of 29 conventional protein kinase sequences in the E. cuniculi genome, as well as 3 genes encoding atypical protein kinases. The microsporidian kinome presents striking differences from those of other eukaryotes, and this minimal kinome underscores the importance of conserved protein kinases involved in essential cellular processes. Approximately 30% of its kinases are predicted to regulate cell cycle progression while another approximately 28% have no identifiable homologues in model eukaryotes and are likely to reflect parasitic adaptations. E. cuniculi lacks MAP kinase cascades and almost all protein kinases that are involved in stress responses, ion homeostasis and nutrient signalling in the model fungi S. cerevisiae and S. pombe, including AMPactivated protein kinase (Snf1), previously thought to be ubiquitous in eukaryotes. A detailed database search and phylogenetic analysis of the kinomes of the two model fungi showed that the degree of homology between their kinomes of approximately 85% is much higher than that previously reported.ConclusionThe E. cuniculi kinome is by far the smallest eukaryotic kinome characterised to date. The difficulty in assigning clear homology relationships for nine out of the twentynine microsporidian conventional protein kinases despite its compact genome reflects the phylogenetic distance between microsporidia and other eukaryotes. Indeed, the E. cuniculi genome presents a high proportion of genes in which evolution has been accelerated by up to four-fold. There are no orthologues of the protein kinases that constitute MAP kinase pathways and many other protein kinases with roles in nutrient signalling are absent from the E. cuniculi kinome. However, orthologous kinases can nonetheless be identified that correspond to members of the yeast kinomes with roles in some of the most fundamental cellular processes. For example, E. cuniculi has clear orthologues of virtually all the major conserved protein kinases that regulate the core cell cycle machinery (Aurora, Polo, DDK, CDK and Chk1). A comprehensive comparison of the homology relationships between the budding and fission yeast kinomes indicates that, despite an estimated 800 million years of independent evolution, the two model fungi share approximately 85% of their protein kinases. This will facilitate the annotation of many of the as yet uncharacterised fission yeast kinases, and also those of novel fungal genomes.

Dataset Information

The SpGAR1 gene of Schizosaccharomyces pombe encodes the functional homologue of the snoRNP protein GAR1 of Saccharomyces cerevisiae.

Publications

The SpGAR1 gene of Schizosaccharomyces pombe encodes the functional homologue of the snoRNP protein GAR1 of Saccharomyces cerevisiae.

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