A Link between Secretion and Pre-mRNA Processing Defects in Saccharomyces cerevisiae and the Identification of a Novel Splicing Gene, RSE1

ABSTRACT Secretory proteins in eukaryotic cells are transported to the cell surface via the endoplasmic reticulum (ER) and the Golgi apparatus by membrane-bounded vesicles. We screened a collection of temperature-sensitive mutants of Saccharomyces cerevisiaefor defects in ER-to-Golgi transport. Two of the genes identified in this screen were PRP2, which encodes a known pre-mRNA splicing factor, and RSE1, a novel gene that we show to be important for pre-mRNA splicing. Both prp2-13 andrse1-1 mutants accumulate the ER forms of invertase and the vacuolar protease CPY at restrictive temperature. The secretion defect in each mutant can be suppressed by increasing the amount ofSAR1, which encodes a small GTPase essential for COPII vesicle formation from the ER, or by deleting the intron from theSAR1 gene. These data indicate that a failure to spliceSAR1 pre-mRNA is the specific cause of the secretion defects in prp2-13 and rse1-1. Moreover, these data imply that Sar1p is a limiting component of the ER-to-Golgi transport machinery and suggest a way that secretory pathway function might be coordinated with the amount of gene expression in a cell.

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Sec35p, a Novel Peripheral Membrane Protein, Is Required for ER to Golgi Vesicle Docking

The Journal of Cell Biology ◽

10.1083/jcb.141.5.1107 ◽

1998 ◽

Vol 141 (5) ◽

pp. 1107-1119 ◽

Cited By ~ 111

Author(s):

Susan M. VanRheenen ◽

Xiaochun Cao ◽

Vladimir V. Lupashin ◽

Charles Barlowe ◽

M. Gerard Waters

Keyword(s):

Secretory Pathway ◽

Genetic Relationships ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Dominant Form ◽

Yeast Saccharomyces Cerevisiae ◽

Vesicle Docking ◽

Genes Encoding ◽

A Cell ◽

Cold Sensitive

SEC35 was identified in a novel screen for temperature-sensitive mutants in the secretory pathway of the yeast Saccharomyces cerevisiae (Wuestehube et al., 1996. Genetics. 142:393–406). At the restrictive temperature, the sec35-1 strain exhibits a transport block between the ER and the Golgi apparatus and accumulates numerous vesicles. SEC35 encodes a novel cytosolic protein of 32 kD, peripherally associated with membranes. The temperature-sensitive phenotype of sec35-1 is efficiently suppressed by YPT1, which encodes the rab-like GTPase required early in the secretory pathway, or by SLY1-20, which encodes a dominant form of the ER to Golgi target -SNARE–associated protein Sly1p. Weaker suppression is evident upon overexpression of genes encoding the vesicle-SNAREs SEC22, BET1, or YKT6. The cold-sensitive lethality that results from deleting SEC35 is suppressed by YPT1 or SLY1-20. These genetic relationships suggest that Sec35p acts upstream of, or in conjunction with, Ypt1p and Sly1p as was previously found for Uso1p. Using a cell-free assay that measures distinct steps in vesicle transport from the ER to the Golgi, we find Sec35p is required for a vesicle docking stage catalyzed by Uso1p. These genetic and biochemical results suggest Sec35p acts with Uso1p to dock ER-derived vesicles to the Golgi complex.

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Cloning of the RNA8 gene of Saccharomyces cerevisiae, detection of the RNA8 protein, and demonstration that it is essential for nuclear pre-mRNA splicing.

Molecular and Cellular Biology ◽

10.1128/mcb.8.3.1067 ◽

1988 ◽

Vol 8 (3) ◽

pp. 1067-1075 ◽

Cited By ~ 30

Author(s):

S P Jackson ◽

M Lossky ◽

J D Beggs

Keyword(s):

Saccharomyces Cerevisiae ◽

Mrna Splicing ◽

Growth Defect ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Cell Extracts ◽

In Vitro Splicing ◽

Essential Function ◽

Beta Galactosidase

Strains of Saccharomyces cerevisiae that bear the temperature-sensitive mutation rna8-1 are defective in nuclear pre-mRNA splicing at the restrictive temperature (36 degrees C), suggesting that the RNA8 gene encodes a component of the splicing machinery. The RNA8 gene was cloned by complementation of the temperature-sensitive growth defect of an rna8-1 mutant strain. Integrative transformation and gene disruption experiments confirmed the identity of the cloned DNA and demonstrated that the RNA8 gene encodes an essential function. The RNA8 gene was shown to be represented once per S. cerevisiae haploid genome and to encode a low-abundance transcript of approximately 7.4 kilobases. By using antisera raised against beta-galactosidase-RNA8 fusion proteins, the RNA8 gene product was identified in S. cerevisiae cell extracts as a low-abundance protein of approximately 260 kilodaltons. Immunodepletion of the RNA8 protein specifically abolished the activity of S. cerevisiae in vitro splicing extracts, confirming that RNA8 plays an essential role in splicing.

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A connection between pre-mRNA splicing and the cell cycle in fission yeast: cdc28+ is allelic with prp8+ and encodes an RNA-dependent ATPase/helicase.

Molecular Biology of the Cell ◽

10.1091/mbc.7.7.1083 ◽

1996 ◽

Vol 7 (7) ◽

pp. 1083-1094 ◽

Cited By ~ 40

Author(s):

K Lundgren ◽

S Allan ◽

S Urushiyama ◽

T Tani ◽

Y Ohshima ◽

...

Keyword(s):

Cell Cycle ◽

Fission Yeast ◽

Growth Arrest ◽

Mrna Splicing ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Yeast Gene ◽

Temperature Sensitive Mutants ◽

Cycle Arrest ◽

A Cell

The fission-yeast gene cdc28+ was originally identified in a screen for temperature-sensitive mutants that exhibit a cell-division cycle arrest and was found to be required for mitosis. We undertook a study of this gene to understand more fully the general requirements for entry into mitosis. Cells carrying the conditional lethal cdc28-P8 mutation divide once and arrest in G2 after being shifted to the restrictive temperature. We cloned the cdc28+ gene by complementation of the temperature-sensitive growth arrest in cdc28-P8. DNA sequence analysis indicated that cdc28+ encodes a member of the DEAH-box family of putative RNA-dependent ATPases or helicases. The Cdc28 protein is most similar to the Prp2, Prp16, and Prp22 proteins from budding yeast, which are required for the splicing of mRNA precursors. Consistent with this similarity, the cdc28-P8 mutant accumulates unspliced precursors at the restrictive temperature. Independently, we isolated a temperature-sensitive pre-mRNA splicing mutant prp8-1 that exhibits a cell-cycle phenotype identical to that of cdc28-P8. We have shown that cdc28 and prp8 are allelic. These results suggest a connection between pre-mRNA splicing and progression through the cell cycle.

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Cloning of the RNA8 gene of Saccharomyces cerevisiae, detection of the RNA8 protein, and demonstration that it is essential for nuclear pre-mRNA splicing

Molecular and Cellular Biology ◽

10.1128/mcb.8.3.1067-1075.1988 ◽

1988 ◽

Vol 8 (3) ◽

pp. 1067-1075

Author(s):

S P Jackson ◽

M Lossky ◽

J D Beggs

Keyword(s):

Saccharomyces Cerevisiae ◽

Mrna Splicing ◽

Growth Defect ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Cell Extracts ◽

In Vitro Splicing ◽

Essential Function ◽

Beta Galactosidase

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Requirement for Three Novel Protein Complexes in the Absence of the Sgs1 DNA Helicase in Saccharomyces cerevisiae

Genetics ◽

10.1093/genetics/157.1.103 ◽

2001 ◽

Vol 157 (1) ◽

pp. 103-118 ◽

Cited By ~ 16

Author(s):

Janet R Mullen ◽

Vivek Kaliraman ◽

Samer S Ibrahim ◽

Steven J Brill

Keyword(s):

Saccharomyces Cerevisiae ◽

Genome Stability ◽

Protein Complexes ◽

Ring Finger ◽

Dna Helicase ◽

Open Reading Frames ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Dna Helicases ◽

Cell Extracts

Abstract The Saccharomyces cerevisiae Sgs1 protein is a member of the RecQ family of DNA helicases and is required for genome stability, but not cell viability. To identify proteins that function in the absence of Sgs1, a synthetic-lethal screen was performed. We obtained mutations in six complementation groups that we refer to as SLX genes. Most of the SLX genes encode uncharacterized open reading frames that are conserved in other species. None of these genes is required for viability and all SLX null mutations are synthetically lethal with mutations in TOP3, encoding the SGS1-interacting DNA topoisomerase. Analysis of the null mutants identified a pair of genes in each of three phenotypic classes. Mutations in MMS4 (SLX2) and SLX3 generate identical phenotypes, including weak UV and strong MMS hypersensitivity, complete loss of sporulation, and synthetic growth defects with mutations in TOP1. Mms4 and Slx3 proteins coimmunoprecipitate from cell extracts, suggesting that they function in a complex. Mutations in SLX5 and SLX8 generate hydroxyurea sensitivity, reduced sporulation efficiency, and a slow-growth phenotype characterized by heterogeneous colony morphology. The Slx5 and Slx8 proteins contain RING finger domains and coimmunoprecipitate from cell extracts. The SLX1 and SLX4 genes are required for viability in the presence of an sgs1 temperature-sensitive allele at the restrictive temperature and Slx1 and Slx4 proteins are similarly associated in cell extracts. We propose that the MMS4/SLX3, SLX5/8, and SLX1/4 gene pairs encode heterodimeric complexes and speculate that these complexes are required to resolve recombination intermediates that arise in response to DNA damage, during meiosis, and in the absence of SGS1/TOP3.

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The Mitochondrial Nucleoid Protein, Mgm101p, of Saccharomyces cerevisiae Is Involved in the Maintenance of ρ+ and ori/rep-Devoid Petite Genomes but Is Not Required for Hypersuppressive ρ− mtDNA

Genetics ◽

10.1093/genetics/160.4.1389 ◽

2002 ◽

Vol 160 (4) ◽

pp. 1389-1400

Author(s):

Xiao Ming Zuo ◽

G Desmond Clark-Walker ◽

Xin Jie Chen

Keyword(s):

Saccharomyces Cerevisiae ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Mitochondrial Rna ◽

Mtdna Copy Number ◽

Mitochondrial Rna Polymerase ◽

Mitochondrial Nucleoids ◽

Mtdna Replication ◽

Sensitive Allele ◽

Discriminatory Effect

Abstract The Saccharomyces cerevisiae MGM101 gene encodes a DNA-binding protein targeted to mitochondrial nucleoids. MGM101 is essential for maintenance of a functional ρ+ genome because meiotic segregants, with a disrupted mgm101 allele, cannot undergo more than 10 divisions on glycerol medium. Quantitative analysis of mtDNA copy number in a ρ+ strain carrying a temperature-sensitive allele, mgm101-1, revealed that the amount of mtDNA is halved each cell division upon a shift to the restrictive temperature. These data suggest that mtDNA replication is rapidly blocked in cells lacking MGM101. However, a small proportion of meiotic segregants, disrupted in MGM101, have ρ− genomes that are stably maintained. Interestingly, all surviving ρ− mtDNAs contain an ori/rep sequence. Disruption of MGM101 in hypersuppressive (HS) strains does not have a significant effect on the propagation of HS ρ− mtDNA. However, in petites lacking an ori/rep, disruption of MGM101 leads to either a complete loss or a dramatically decreased stability of mtDNA. This discriminatory effect of MGM101 suggests that replication of ρ+ and ori/rep-devoid ρ− mtDNAs is carried out by the same process. By contrast, the persistence of ori/rep-containing mtDNA in HS petites lacking MGM101 identifies a distinct replication pathway. The alternative mtDNA replication mechanism provided by ori/rep is independent of mitochondrial RNA polymerase encoded by RPO41 as a HS ρ− genome is stably maintained in a mgm101, rpo41 double mutant.

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DBF8, an essential gene required for efficient chromosome segregation in Saccharomyces cerevisiae

Molecular and Cellular Biology ◽

10.1128/mcb.14.9.6350-6360.1994 ◽

1994 ◽

Vol 14 (9) ◽

pp. 6350-6360

Author(s):

F Houman ◽

C Holm

Keyword(s):

Saccharomyces Cerevisiae ◽

Chromosome Segregation ◽

Mutational Analysis ◽

Essential Gene ◽

Chromosome Loss ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

Permissive Temperature ◽

Nonsense Mutations ◽

Carboxy Terminal

To investigate chromosome segregation in Saccharomyces cerevisiae, we examined a collection of temperature-sensitive mutants that arrest as large-budded cells at restrictive temperatures (L. H. Johnston and A. P. Thomas, Mol. Gen. Genet. 186:439-444, 1982). We characterized dbf8, a mutation that causes cells to arrest with a 2c DNA content and a short spindle. DBF8 maps to chromosome IX near the centromere, and it encodes a 36-kDa protein that is essential for viability at all temperatures. Mutational analysis reveals that three dbf8 alleles are nonsense mutations affecting the carboxy-terminal third of the encoded protein. Since all of these mutations confer temperature sensitivity, it appears that the carboxyl-terminal third of the protein is essential only at a restrictive temperature. In support of this conclusion, an insertion of URA3 at the same position also confers a temperature-sensitive phenotype. Although they show no evidence of DNA damage, dbf8 mutants exhibit increased rates of chromosome loss and nondisjunction even at a permissive temperature. Taken together, our data suggest that Dbf8p plays an essential role in chromosome segregation.

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Regulated and constitutive secretion of distinct molecular forms of acetylcholinesterase from PC12 cells

Journal of Cell Science ◽

10.1242/jcs.106.3.731 ◽

1993 ◽

Vol 106 (3) ◽

pp. 731-740 ◽

Cited By ~ 2

Author(s):

E.S. Schweitzer

Keyword(s):

Pc12 Cells ◽

Secretory Pathway ◽

Intracellular Localization ◽

Synaptic Function ◽

Molecular Forms ◽

Secretory Proteins ◽

Secretory Pathways ◽

Regulated Secretion ◽

Constitutive Secretion ◽

A Cell

PC12 cells secrete the enzyme acetylcholinesterase (AChE) while at rest, and increase the overall rate of this secretion 2-fold upon depolarization. This behavior is different from the release of other markers by the constitutive or regulated secretory pathways in PC12 cells. Both the resting and stimulated release of AChE are unchanged after treatment with a membrane-impermeable esterase inhibitor, demonstrating that it represents true secretion and not shedding from the cell surface. The stimulation release of AChE is Ca(2+)-dependent, while the unstimulated release is not. Analysis of the molecular forms of AChE secreted by PC12 cells indicates that the release of AChE actually involves two concurrent but independent secretory processes, and that the G4 form of the enzyme is secreted constitutively, while both the G2 and G4 forms are secreted in a regulated manner, presumably from regulated secretory vesicles. Compared with other regulated secretory proteins, a much smaller fraction of cellular AChE is secreted, and the intracellular localization of this enzyme differs from that of other regulated secretory proteins. The demonstration that a cell line that exhibits regulated secretion of acetylcholine (ACh) is also capable of regulated secretion of AChE provides additional evidence for the existence of multiple regulated secretory pathways within a single cell. Moreover, there appears to be a selective packaging of different molecular forms of AChE into the regulated versus the constitutive secretory pathway. Both the specificity of sorting of AChE and the regulation of its secretion suggest that AChE may play a more dynamic role in synaptic function than has been recognized previously.

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Cell cycle arrest of cdc mutants and specificity of the RAD9 checkpoint.

Genetics ◽

10.1093/genetics/134.1.63 ◽

1993 ◽

Vol 134 (1) ◽

pp. 63-80 ◽

Cited By ~ 9

Author(s):

T A Weinert ◽

L H Hartwell

Keyword(s):

Cell Cycle ◽

Cell Division ◽

Dna Replication ◽

Cell Cycle Control ◽

Dna Lesions ◽

Temperature Sensitive ◽

Restrictive Temperature ◽

A Cell ◽

G2 Phase ◽

Rad Mutants

Abstract In eucaryotes a cell cycle control called a checkpoint ensures that mitosis occurs only after chromosomes are completely replicated and any damage is repaired. The function of this checkpoint in budding yeast requires the RAD9 gene. Here we examine the role of the RAD9 gene in the arrest of the 12 cell division cycle (cdc) mutants, temperature-sensitive lethal mutants that arrest in specific phases of the cell cycle at a restrictive temperature. We found that in four cdc mutants the cdc rad9 cells failed to arrest after a shift to the restrictive temperature, rather they continued cell division and died rapidly, whereas the cdc RAD cells arrested and remained viable. The cell cycle and genetic phenotypes of the 12 cdc RAD mutants indicate the function of the RAD9 checkpoint is phase-specific and signal-specific. First, the four cdc RAD mutants that required RAD9 each arrested in the late S/G2 phase after a shift to the restrictive temperature when DNA replication was complete or nearly complete, and second, each leaves DNA lesions when the CDC gene product is limiting for cell division. Three of the four CDC genes are known to encode DNA replication enzymes. We found that the RAD17 gene is also essential for the function of the RAD9 checkpoint because it is required for phase-specific arrest of the same four cdc mutants. We also show that both X- or UV-irradiated cells require the RAD9 and RAD17 genes for delay in the G2 phase. Together, these results indicate that the RAD9 checkpoint is apparently activated only by DNA lesions and arrests cell division only in the late S/G2 phase.

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Distinct Roles for the Yeast Phosphatidylinositol 4-Kinases, Stt4p and Pik1p, in Secretion, Cell Growth, and Organelle Membrane Dynamics

Molecular Biology of the Cell ◽

10.1091/mbc.11.8.2673 ◽

2000 ◽

Vol 11 (8) ◽

pp. 2673-2689 ◽

Cited By ~ 254

Author(s):

Anjon Audhya ◽

Michelangelo Foti ◽

Scott D. Emr

Keyword(s):

Cell Growth ◽

Membrane Trafficking ◽

Secretory Pathway ◽

Membrane Dynamics ◽

Small Gtpase ◽

Effector Proteins ◽

Restrictive Temperature ◽

Yeast Saccharomyces Cerevisiae ◽

Cytoskeleton Organization ◽

Yeast Viability

The yeast Saccharomyces cerevisiae possesses two genes that encode phosphatidylinositol (PtdIns) 4-kinases,STT4 and PIK1. Both gene products phosphorylate PtdIns at the D-4 position of the inositol ring to generate PtdIns(4)P, which plays an essential role in yeast viability because deletion of either STT4 orPIK1 is lethal. Furthermore, although both enzymes have the same biochemical activity, increased expression of either kinase cannot compensate for the loss of the other, suggesting that these kinases regulate distinct intracellular functions, each of which is required for yeast cell growth. By the construction of temperature-conditional single and double mutants, we have found that Stt4p activity is required for the maintenance of vacuole morphology, cell wall integrity, and actin cytoskeleton organization. In contrast, Pik1p is essential for normal secretion, Golgi and vacuole membrane dynamics, and endocytosis. Strikingly,pik1tscells exhibit a rapid defect in secretion of Golgi-modified secretory pathway cargos, Hsp150p and invertase, whereas stt4tscells exhibit no detectable secretory defects. Both single mutants reduce PtdIns(4)P by ∼50%; however,stt4ts/pik1tsdouble mutant cells produce more than 10-fold less PtdIns(4)P as well as PtdIns(4,5)P2. The aberrant Golgi morphology found in pik1tsmutants is strikingly similar to that found in cells lacking the function of Arf1p, a small GTPase that is known to regulate multiple membrane trafficking events throughout the cell. Consistent with this observation, arf1 mutants exhibit reduced PtdIns(4)P levels. In contrast, diminished levels of PtdIns(4)P observed in stt4tscells at restrictive temperature result in a dramatic change in vacuole size compared with pik1tscells and persistent actin delocalization. Based on these results, we propose that Stt4p and Pik1p act as the major, if not the only, PtdIns 4-kinases in yeast and produce distinct pools of PtdIns(4)P and PtdIns(4,5)P2that act on different intracellular membranes to recruit or activate as yet uncharacterized effector proteins.

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