Biomedical subjects

C A Styles

Publications and source records attributed to C A Styles.

14 recordsLinked to original sources

PubMed1997

MAP kinases with distinct inhibitory functions impart signaling specificity during yeast differentiation.

Filamentous invasive growth of S. cerevisiae requires multiple elements of the mitogen-activated protein kinase (MAPK) signaling cascade that are also components of the mating pheromone response pathway. Here we show that, despite sharing several constituents, the two pathways use different MAP kinases. The Fus3 MAPK regulates mating, whereas the Kss1 MAPK regulates filamentation and invasion. Remarkably, in addition to their kinase-dependent activation functions, Kss1 and Fus3 each have a distinct kinase-independent inhibitory function. Kss1 inhibits the filamentation pathway by interacting with its target transcription factor Ste12. Fus3 has a different inhibitory activity that prevents the inappropriate activation of invasion by the pheromone response pathway. In the absence of Fus3, there is erroneous crosstalk in which mating pheromone now activates filamentation-specific gene expression using the Kss1 MAPK.

Amino Acids↗

PubMed1996

Saccharomyces cerevisiae S288C has a mutation in FLO8, a gene required for filamentous growth.

Diploid strains of baker's yeast Saccharomyces cerevisiae can grow in a cellular yeast form or in filaments called pseudohyphae. This dimorphic transition from yeast to pseudohyphae is induced by starvation for nitrogen. Not all laboratory strains are capable of this dimorphic switch; many grow only in the yeast form and fail to form pseudohyphae when starved for nitrogen. Analysis of the standard laboratory strain S288C shows that this defect in dimorphism results from a nonsense mutation in the FLO8 gene. This defect in FLO8 blocks pseudohyphal growth in diploids, haploid invasive growth, and flocculation. Since feral strains of S. cerevisiae are dimorphic and have a functional FLO8 gene, we suggest that the flo8 mutation was selected during laboratory cultivation.

Alleles↗

PubMed1994

Symmetric cell division in pseudohyphae of the yeast Saccharomyces cerevisiae.

Laboratory strains of Saccharomyces cerevisiae are dimorphic; in response to nitrogen starvation they switch from a yeast form (YF) to a filamentous pseudohyphal (PH) form. Time-lapse video microscopy of dividing cells reveals that YF and PH cells differ in their cell cycles and budding polarity. The YF cell cycle is controlled at the G1/S transition by the cell-size checkpoint Start. YF cells divide asymmetrically, producing small daughters from full-sized mothers. As a result, mothers and daughters bud asynchronously. Mothers bud immediately but daughters grow in G1 until they achieve a critical cell size. By contrast, PH cells divide symmetrically, restricting mitosis until the bud grows to the size of the mother. Thus, mother and daughter bud synchronously in the next cycle, without a G1 delay before Start. YF and PH cells also exhibit distinct bud-site selection patterns. YF cells are bipolar, producing their second and subsequent buds at either pole. PH cells are unipolar, producing their second and subsequent buds only from the end opposite the junction with their mother. We propose that in PH cells a G2 cell-size checkpoint delays mitosis until bud size reaches that of the mother cell. We conclude that yeast and PH forms are distinct cell types each with a unique cell cycle, budding pattern, and cell shape.

Actins↗

PubMed1993

Elements of the yeast pheromone response pathway required for filamentous growth of diploids.

Transmission of an external signal from receptors to downstream targets is often mediated by a conserved set of protein kinases that act in sequence (a kinase cascade). In haploid strains of Saccharomyces cerevisiae, a signal initiated by peptide pheromones is transmitted through this kinase cascade to a transcription factor STE12, which is required for the expression of many mating-specific genes. Here it was shown that in diploids some of the same kinases and STE12 are required for filamentous growth, but the pheromone receptors and guanosine triphosphate-binding protein are not required for filament formation. Thus, a similar kinase cascade is activated by different signals in haploids and diploids and mediates different developmental outcomes in the two cell types.

Fungal Proteins↗

PubMed1992

SHR3: a novel component of the secretory pathway specifically required for localization of amino acid permeases in yeast.

Mutations in SHR3 block amino acid uptake into yeast by reducing the levels of multiple amino acid permeases within the plasma membrane. SHR3 is a novel integral membrane protein component of the endoplasmic reticulum (ER). shr3 null mutants specifically accumulate amino acid permeases in the ER; other plasma membrane proteins, secretory proteins, and vacuolar proteins are processed and targeted correctly. Our findings suggest that SHR3 interacts with a structural domain shared by amino acid permeases, an interaction required for permease-specific processing and transport from the ER. Even in the presence of excess amino acids, shr3 mutants exhibit starvation responses. shr3 mutants constitutively express elevated levels of GCN4, and mutant shr3/shr3 diploids undergo dimorphic transitions that result in filamentous growth at enhanced frequencies.

Amino Acid Sequence↗

PubMed1992

Unipolar cell divisions in the yeast S. cerevisiae lead to filamentous growth: regulation by starvation and RAS.

Diploid S. cerevisiae strains undergo a dimorphic transition that involves changes in cell shape and the pattern of cell division and results in invasive filamentous growth in response to starvation for nitrogen. Cells become long and thin and form pseudohyphae that grow away from the colony and invade the agar medium. Pseudohyphal growth allows yeast cells to forage for nutrients. Pseudohyphal growth requires the polar budding pattern of a/alpha diploid cells; haploid axially budding cells of identical genotype cannot undergo this dimorphic transition. Constitutive activation of RAS2 or mutation of SHR3, a gene required for amino acid uptake, enhance the pseudohyphal phenotype; a dominant mutation in RSR1/BUD1 that causes random budding suppresses pseudohyphal growth.

Cell Division↗

PubMed1990

BIK1, a protein required for microtubule function during mating and mitosis in Saccharomyces cerevisiae, colocalizes with tubulin.

BIK1 function is required for nuclear fusion, chromosome disjunction, and nuclear segregation during mitosis. The BIK1 protein colocalizes with tubulin to the spindle pole body and mitotic spindle. Synthetic lethality observed in double mutant strains containing a mutation in the BIK1 gene and in the gene for alpha- or beta-tubulin is consistent with a physical interaction between BIK1 and tubulin. Furthermore, over- or underexpression of BIK1 causes aberrant microtubule assembly and function, bik1 null mutants are viable but contain very short or undetectable cytoplasmic microtubules. Spindle formation often occurs strictly within the mother cell, probably accounting for the many multinucleate and anucleate bik1 cells. Elevated levels of chromosome loss in bik1 cells are indicative of defective spindle function. Nuclear fusion is blocked in bik1 x bik1 zygotes, which have truncated cytoplasmic microtubules. Cells overexpressing BIK1 initially have abnormally short or nonexistent spindle microtubules and long cytoplasmic microtubules. Subsequently, cells lose all microtubule structures, coincident with the arrest of division. Based on these results, we propose that BIK1 is required stoichiometrically for the formation or stabilization of microtubules during mitosis and for spindle pole body fusion during conjugation.

Amino Acid Sequence↗

PubMed1989

A suppressor of a HIS4 transcriptional defect encodes a protein with homology to the catalytic subunit of protein phosphatases.

Reversion analysis has identified four suppressor genes that permit transcription of the Saccharomyces cerevisiae HIS4 gene in the absence of GCN4, BAS1, and BAS2, trans-acting proteins normally required for activation of HIS4 transcription. These suppressor genes encode factors that affect the transcription of many diverse genes. Two of these suppressors, SIT1 and SIT2, are encoded by RPB1 and RPB2, the genes for the two largest subunits of RNA polymerase II. All strains containing suppressor mutations in RPB1 and RPB2 have reduced transcription of the INO1 gene and an inositol requirement. Mutations in SIT3 or high copy number SIT3 increase HIS4 transcription in the absence of GCN4, BAS1, and BAS2. This increase in HIS4 transcription by high copy number SIT3 or by sit3 alleles is largely independent of the HIS4 TATA sequence. The SIT4 protein is over 50% identical to the catalytic subunit of bovine type 2A protein phosphatase. sit4 mutations in combination with suppressor mutations in RPB1 or RPB2 (sit1, sit4 or sit2, sit4) are lethal, suggesting an interaction between SIT4 and RNA polymerase II.

Amino Acid Sequence↗

PubMed1988

TRK1 encodes a plasma membrane protein required for high-affinity potassium transport in Saccharomyces cerevisiae.

We identified a 180-kilodalton plasma membrane protein in Saccharomyces cerevisiae required for high-affinity transport (uptake) of potassium. The gene that encodes this putative potassium transporter (TRK1) was cloned by its ability to relieve the potassium transport defect in trk1 cells. TRK1 encodes a protein 1,235 amino acids long that contains 12 potential membrane-spanning domains. Our results demonstrate the physical and functional independence of the yeast potassium and proton transport systems. TRK1 is nonessential in S. cerevisiae and maps to a locus unlinked to PMA1, the gene that encodes the plasma membrane ATPase. Haploid cells that contain a null allele of TRK1 (trk1 delta) rely on a low-affinity transporter for potassium uptake and, under certain conditions, exhibit energy-dependent loss of potassium, directly exposing the activity of a transporter responsible for the efflux of this ion.

Base Sequence↗

PubMed1986

Saccharomyces cerevisiae SPT3 gene is required for transposition and transpositional recombination of chromosomal Ty elements.

Mutations in the Saccharomyces cerevisiae SPT3 gene have dramatic effects on the expression of Ty elements and genes adjacent to the element. The SPT3 gene is essential for Ty transposition, because transposition of chromosomal Ty elements ceased when the SPT3 gene was replaced with the frameshift mutation spt3-101. Presumably, the elimination of transposition was due to the effect of the SPT3 gene product on Ty transcription; the transcripts of chromosomal Ty elements were largely abolished in the spt3-101 strain (F. Winston, K. J. Durbin, and G. R. Fink, Cell 39:675-682, 1984). Ty transcription in an spt3-101 strain could be reestablished by introduction of the pGTyH3 plasmid, in which transcription of the Ty element TyH3 is under the control of the GAL1 promoter; these plasmid-derived Ty transcripts were SPT3-independent. Ty transposition resumed after galactose induction in spt3-101 strains containing the pGTyH3 plasmid. In spt3 mutants nearly all of the resulting transposition events derived from pGTyH3 plasmids and not from chromosomal elements.

Chromosome Mapping↗

PubMed1985

Ty elements transpose through an RNA intermediate.

We have followed Ty transposition with a donor Ty element, TyH3, whose expression is under the control of the GAL1 promoter. Sequence analysis reveals dramatic structural differences in TyH3 before and after transposition. If the donor TyH3 is marked with an intron-containing fragment, the intron is correctly spliced out of the Ty during transposition, suggesting that the Ty RNA is the intermediate for transposition. Furthermore, the pattern of sequence inheritance in progeny Ty insertions derived from the marked Ty follows the predictions of the model of retroviral reverse transcription. Comparison of marked Ty elements before and after movement shows that transposition is highly mutagenic to the Ty element. These results demonstrate that during transposition, Ty sequence information flows from DNA to RNA to DNA.

Base Sequence↗

PubMed1984

Ty-mediated gene expression of the LYS2 and HIS4 genes of Saccharomyces cerevisiae is controlled by the same SPT genes.

Five Ty insertion mutations were isolated at the LYS2 locus of Saccharomyces cerevisiae. Genetic and physical analyses show that four Ty insertions are in the 5' noncoding region of LYS2 and one is within the structural gene. Three of these Ty elements have been cloned and characterized. The Ty mutations differ from each other in restriction pattern, phenotypic effects on LYS2, reversion frequency, and the nature of reversion events. Spt2 and spt3 mutations, known to suppress Ty insertions and their solo delta derivatives at HIS4, can also suppress at least one of the Ty insertions (Ty61) at LYS2 and can also suppress the Lys- phenotype of a solo delta derivative of another Ty insertion (Ty128) at LYS2. These results demonstrate that spt mutations can suppress Ty and delta mutations at both HIS4 and LYS2, suggesting that they are general for their effects on Ty and delta elements.

Cloning, Molecular↗

PubMed1974

Gene conversion of deletions in the his4 region of yeast.

A selection procedure has been devised which allows the recovery of deletions of the his4 region of Saccharomyces cerevisiae. Many deletions were obtained by this procedure and were characterized genetically and biochemically. These deletions permit the construction of a linear map of the his4A and his4B region. A deletion which was large on this genetic map reduced the size of the his4 gene product. Tetrad analyses revealed that deletions can affect the conversion frequency of other alleles at his4. Analysis of reciprocal recombination in conversion tetrads showed that the order of genes on chromosome III is: centromere-leu2-his4A-his4C. This means that in his4 transcription and translation proceed away from the centromere.

Chromosome Mapping↗

PubMed1972

Curing of a killer factor in Saccharomyces cerevisiae.

Many standard laboratory stocks of yeast are able to kill other yeast strains. This property has not been generally recognized because killing is observed only at low pH and not at the pH of standard media. In all strains examined, the genetic determinant for the killer trait shows non-Mendelian inheritance. The segregation patterns of our killer strains indicate that this killer determinant may be different from the killer previously described. Treatment of a killer strain with cycloheximide, but not with ethidium bromide, converts it into a sensitive nonkiller.

Antibiosis↗