bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dtr1p, a Multidrug Resistance Transporter of the Major Facilitator Superfamily, Plays an Essential Role in Spore Wall Maturation in
Saccharomyces cerevisiae
Authors: Felder Thomas , Bogengruber Edith , Tenreiro Sandra , Ellinger Adi , Sá-Correia Isabel , Briza Peter 
Published: December 2002

ABSTRACT

The de novo formation of multilayered spore walls inside a diploid mother cell is a major landmark of sporulation in the yeast
Saccharomyces cerevisiae
. Synthesis of the dityrosine-rich outer spore wall takes place toward the end of this process. Bisformyl dityrosine, the major building block of the spore surface, is synthesized in a multistep process in the cytoplasm of the prospores, transported to the maturing wall, and polymerized into a highly cross-linked macromolecule on the spore surface. Here we present evidence that the sporulation-specific protein Dtr1p (encoded by
YBR180w
) plays an important role in spore wall synthesis by facilitating the translocation of bisformyl dityrosine through the prospore membrane.
DTR1
was identified in a genome-wide screen for spore wall mutants. The null mutant accumulates unusually large amounts of bisformyl dityrosine in the cytoplasm and fails to efficiently incorporate this precursor into the spore surface. As a result, many mutant spores have aberrant surface structures. Dtr1p, a member of the poorly characterized DHA12 (drug:H
+
antiporter with 12 predicted membrane spans) family, is localized in the prospore membrane throughout spore maturation. Transport by Dtr1p may not be restricted to its natural substrate, bisformyl dityrosine. When expressed in vegetative cells, Dtr1p renders these cells slightly more resistant against unrelated toxic compounds, such as antimalarial drugs and food-grade organic acid preservatives. Dtr1p is the first multidrug resistance protein of the major facilitator superfamily with an assigned physiological role in the yeast cell.
Maintenance of Mating Cell Integrity Requires the Adhesin Fig2p
Authors: Zhang Mingliang , Bennett Daniel , Erdman Scott E. 
Published: December 2002

ABSTRACT

Fungal adhesins represent a large family of serine/threonine-rich secreted glycoproteins. Adhesins have been shown to play roles in heterotypic and homotypic cell-cell adhesion processes, morphogenetic pathways and invasive/pseudohyphal growth, frequently in response to differentiation cues. Here we address the role of the
Saccharomyces cerevisiae
mating-specific adhesin Fig2p. Cells lacking
FIG2
possess a variety of mating defects that relate to processes involving the cell wall, including morphogenetic defects, cell fusion defects, and alterations in agglutination activities. We found that mating-specific morphogenetic defects caused by the absence of
FIG2
are suppressible by increased external osmolarity and that, during mating,
fig2
Δ cells display reduced viability relative to wild-type cells. These defects result from alterations in signaling activated by the mating and cell integrity pathways. Finally, we show that
fig2
Δ zygotes also have defects in zygotic spindle positioning that are osmoremedial, whereas the requirements for
FIG2
in normal cell-cell agglutination and cell fusion during mating are insensitive to changes in the extracellular osmotic environment. We conclude that
FIG2
performs distinct functions in the mating cell wall that are separable with respect to their ability to be suppressed by changes in external osmolarity and that a fundamental role of
FIG2
in mating cells is the maintenance of cell integrity.
Conidiation in
Penicillium cyclopium
Is Induced by Conidiogenone, an Endogenous Diterpene
Authors: Roncal Tomás , Cordobés Shandra , Sterner Olov , Ugalde Unai 
Published: December 2002

ABSTRACT

The filamentous fungus
Penicillium cyclopium
conidiates in the presence of calcium ions in submerged culture without nutrient limitation according to a precisely timed program. Conidiation could be prematurely induced in a nutritionally sufficient medium which had previously supported growth, suggesting that a metabolite which influenced the process was produced. A diterpenoid with conidiation-inducing activity, conidiogenone, was purified from the culture medium, along with conidiogenol, a putative derivative with delayed activity. Contrary to previous thought, the presence of calcium was demonstrated to only decrease the threshold concentration of conidiogenone required for the induction to proceed. In light of these results, a mechanism of conidiation induction is presented according to which the mycelium produces a conidiation inducer (conidiogenone) that accumulates extracellularly. When a threshold concentration is reached, induction likely takes place by interaction with a specific cellular receptor. The results indicate that conidiogenone is both sufficient and necessary to induce conidiation.
The Yeast Paf1-RNA Polymerase II Complex Is Required for Full Expression of a Subset of Cell Cycle-Regulated Genes
Authors: Porter Stephanie E. , Washburn Taylor M. , Chang Meiping , Jaehning Judith A. 
Published: December 2002

ABSTRACT

We have previously described an alternative form of RNA polymerase II in yeast lacking the Srb and Med proteins but including Paf1, Cdc73, Hpr1, and Ccr4. The Paf1-RNA polymerase II complex (Paf1 complex) acts in the same pathway as the Pkc1-mitogen-activated protein kinase cascade and is required for full expression of many cell wall biosynthetic genes. The expression of several of these cell integrity genes, as well as many other Paf1-requiring genes identified by differential display and microarray analyses, is regulated during the cell cycle. To determine whether the Paf1 complex is required for basal or cyclic expression of these genes, we assayed transcript abundance throughout the cell cycle. We found that transcript abundance for a subset of cell cycle-regulated genes, including
CLN1
,
HO
,
RNR1
, and
FAR1
, is reduced from 2- to 13-fold in a
paf1
Δ strain, but that this reduction is not promoter dependent. Despite the decreased expression levels, cyclic expression is still observed. We also examined the possibility that the Paf1 complex acts in the same pathway as either SBF (Swi4/Swi6) or MBF (Mbp1/Swi6), the partially redundant cell cycle transcription factors. Consistent with the possibility that they have overlapping essential functions, we found that loss of Paf1 is lethal in combination with loss of Swi4 or Swi6. In addition, overexpression of either Swi4 or Mbp1 suppresses some
paf1
Δ phenotypes. These data establish that the Paf1 complex plays an important role in the essential regulatory pathway controlled by SBF and MBF.
Role of Fig2p in Agglutination in
Saccharomyces cerevisiae
Authors: Jue Chong K. , Lipke Peter N. 
Published: December 2002

ABSTRACT

In W303-derived strains, disruption of
FIG2
increased agglutinability of α cells, but not
a
cells, and did not alter expression of α-agglutinin, binding of
125
I-labeled α-agglutinin, or mating efficiency. Fig2p overexpression led to α-cell-specific suppression of agglutinability. These results imply that Fig2p is an indirect masker of the active sites in α-agglutinin.
Ex Vivo and In Vitro Identification of a Consensus Promoter for
VSG
Genes Expressed by Metacyclic-Stage Trypanosomes in the Tsetse Fly
Authors: Ginger Michael L. , Blundell Patricia A. , Lewis Alyson M. , Browitt Alison , Günzl Arthur , Barry J. David 
Published: December 2002

ABSTRACT

The trypanosome variant surface glycoprotein (VSG) is first expressed during differentiation to the infective, metacyclic population in tsetse fly salivary glands. Unlike the
VSG
genes expressed by bloodstream form trypanosomes, metacyclic
VSG
s (
MVSG
s) have their own promoters. The scarcity of metacyclic cells has meant that only indirect approaches have been used to study these promoters, and not even their identities have been agreed on. Here, we isolated trypanosomes by dissection from salivary glands and used an approach involving 5′ rapid amplification of cDNA ends to identify the transcription start site of three
MVSG
s. This shows that the authentic start site is that proposed for the
MVAT
series of
MVSG
s (K. S. Kim and J. E. Donelson, J. Biol. Chem.
272:
24637-24645, 1997). In the more readily accessible procyclic trypanosome stage, where
MVSG
s are normally silent, we used reporter gene assays and linker scanning analysis to confirm that the 67 bp upstream of the start site is a promoter. This is confirmed further by accurate initiation in a homologous in vitro transcription system. We show also that
MVSG
promoters become derepressed when tested outwith their endogenous, subtelomeric loci. The
MVSG
promoters are only loosely conserved with bloodstream
VSG
promoters, and our detailed analysis of the
1.63 MVSG
promoter reveals that its activity depends on the start site itself and sequences 26 to 49 bp and 56 to 60 bp upstream. These are longer than those necessary for the bloodstream promoter.
Deletion of Individual mRNA Capping Genes Is Unexpectedly Not Lethal to
Candida albicans
and Results in Modified mRNA Cap Structures
Authors: Dunyak Donna S. , Everdeen Daniel S. , Albanese Joseph G. , Quinn Cheryl L. 
Published: December 2002

ABSTRACT

Eukaryotic mRNAs are modified at the 5′ end with a cap structure. In fungal cells, the formation of the mRNA cap structure is catalyzed by three enzymes: triphosphatase, guanylyltransferase, and methyltransferase. Fungal capping enzymes have been proposed to be good antifungal targets because they differ significantly from their human counterparts and the genes encoding these enzymes are essential in
Saccharomyces cerevisiae
. In the present study,
Candida albicans
null mutants were constructed for both the mRNA triphosphatase-encoding gene (
CET1
) and the mRNA methyltransferase encoding gene (
CCM1
), proving that these genes are not essential in
C. albicans.
Heterozygous deletions were generated, but no null mutants were isolated for the guanylyltransferase-encoding gene (
CGT1
), indicating that this gene probably is essential in
C. albicans.
Whereas these results indicate that Cet1p and Ccm1p are not ideal molecular targets for development of anticandidal drugs, they do raise questions about the capping of mRNA and translation initiation in this fungus. Southern blot analysis of genomic DNA indicates that there are not redundant genes for
CET1
and
CCM1
and analysis of mRNA cap structures indicate there are not alternative pathways compensating for the function of
CET1
or
CCM1
in the null mutants. Instead, it appears that
C. albicans
can survive with modified mRNA cap structures.
Rvs161p and Sphingolipids Are Required for Actin Repolarization following Salt Stress
Authors: Balguerie Axelle , Bagnat Michel , Bonneu Marc , Aigle Michel , Breton Annick M. 
Published: December 2002

ABSTRACT

In
Saccharomyces cerevisiae
, the actin cytoskeleton is depolarized by NaCl stress. In this study, the response was maximal after 30 min, and then actin patches repolarized. Rvs161p was required for actin repolarization because the
rvs161Δ
mutant did not repolarize actin patches after growth in a salt medium. Mutations suppressing the
rvs161Δ
-related salt sensitivity all occurred in genes required for sphingolipid biosynthesis:
FEN1
,
SUR4
,
SUR2
,
SUR1
, and
IPT1
. These suppressors also suppressed
act1-1
-related salt sensitivity and the defect in actin repolarization of the
rvs161Δ
mutant, providing a link between sphingolipids and actin polarization. Indeed, deletion of the suppressor genes suppressed the
rvs161Δ
defect in actin repolarization in two ways: either actin was not depolarized at the wild-type level in a set of suppressor mutants, or actin was repolarized in the absence of Rvs161p in the other suppressor mutants. Rvs161p was localized as cortical patches that concentrated at polarization sites, i.e., bud emergence and septa, and was found to be associated with lipid rafts. An important link between sphingolipids and actin polarization is that Rvs161p was required for actin repolarization and was found to be located in lipid rafts.
Role of Ptc2 Type 2C Ser/Thr Phosphatase in Yeast High-Osmolarity Glycerol Pathway Inactivation
Authors: Young Christian , Mapes James , Hanneman Jennifer , Al-Zarban Sheikha , Ota Irene 
Published: December 2002

ABSTRACT

Three type 2C Ser/Thr phosphatases (PTCs) are negative regulators of the yeast
Saccharomyces cerevisiae
high-osmolarity glycerol mitogen-activated protein kinase (MAPK) pathway. Ptc2 and Ptc3 are 75% identical to each other and differ from Ptc1 in having a noncatalytic domain. Previously, we showed that Ptc1 inactivates the pathway by dephosphorylating the Hog1 MAPK; Ptc1 maintains low basal Hog1 activity and dephosphorylates Hog1 during adaptation. Here, we examined the function of Ptc2 and Ptc3. First, deletion of
PTC2
and/or
PTC3
together with
PTP2
, encoding the protein tyrosine phosphatase that inactivates Hog1, produced a strong growth defect at 37°C that was dependent on
HOG1
, providing further evidence that
PTC2
and
PTC3
are negative regulators. Second, overexpression of
PTC2
inhibited Hog1 activation but did not affect Hog1-Tyr phosphorylation, suggesting that Ptc2 inactivates the pathway by dephosphorylating the Hog1 activation loop phosphothreonine (pThr) residue. Indeed, in vitro studies confirmed that Ptc2 was specific for Hog1-pThr. Third, deletion of both
PTC2
and
PTC3
led to greater Hog1 activation upon osmotic stress than was observed in wild-type strains, although no obvious change in Hog1 inactivation during adaptation was seen. These results indicate that Ptc2 and Ptc3 differ from Ptc1 in that they limit maximal Hog1 activity. The function of the Ptc2 noncatalytic domain was also examined. Deletion of this domain decreased
V
max
by 1.6-fold and increased

K
m

by 2-fold. Thus Ptc2 requires an additional amino acid sequence beyond the catalytic domain defined for PTCs for full activity.
ROX1
and
ERG
Regulation in
Saccharomyces cerevisiae
: Implications for Antifungal Susceptibility
Authors: Henry Karl W. , Nickels Joseph T. , Edlind Thomas D. 
Published: December 2002

ABSTRACT

Yeasts respond to treatment with azoles and other sterol biosynthesis inhibitors by upregulating the expression of the
ERG
genes responsible for ergosterol production. Previous studies on
Saccharomyces cerevisiae
implicated the
ROX1
repressor in
ERG
regulation. We report that
ROX1
deletion resulted in 2.5- to 16-fold-lower susceptibilities to azoles and terbinafine. In untreated cultures,
ERG11
was maximally expressed in mid-log phase and expression decreased in late log phase, while the inverse was observed for
ROX1
. In azole-treated cultures,
ERG11
upregulation was preceded by a decrease in
ROX1
RNA. These inverse correlations suggest that transcriptional regulation of
ROX1
is an important determinant of
ERG
expression and hence of azole and terbinafine susceptibilities.
Cellulose Synthase (
CesA
) Genes in the Green Alga
Mesotaenium caldariorum
Authors: Roberts Alison W. , Roberts Eric M. , Delmer Deborah P. 
Published: December 2002

ABSTRACT

Cellulose, a microfibrillar polysaccharide consisting of bundles of β-1,4-glucan chains, is a major component of plant and most algal cell walls and is also synthesized by some prokaryotes. Seed plants and bacteria differ in the structures of their membrane terminal complexes that make cellulose and, in turn, control the dimensions of the microfibrils produced. They also differ in the domain structures of their
CesA
gene products (the catalytic subunit of cellulose synthase), which have been localized to terminal complexes and appear to help maintain terminal complex structure. Terminal complex structures in algae range from rosettes (plant-like) to linear forms (bacterium-like). Thus, algal
CesA
genes may reveal domains that control terminal complex assembly and microfibril structure. The
CesA
genes from the alga
Mesotaenium caldariorum
, a member of the order Zygnematales, which have rosette terminal complexes, are remarkably similar to seed plant
CesA
s, with deduced amino acid sequence identities of up to 59%. In addition to the putative transmembrane helices and the D-D-D-QXXRW motif shared by all known
CesA
gene products,
M. caldariorum
and seed plant CesAs share a region conserved among plants, an N-terminal zinc-binding domain, and a variable or class-specific region. This indicates that the domains that characterize seed plant CesAs arose prior to the evolution of land plants and may play a role in maintaining the structures of rosette terminal complexes. The
CesA
genes identified in
M. caldariorum
are the first reported for any eukaryotic alga and will provide a basis for analyzing the
CesA
genes of algae with different types of terminal complexes.
Hyphal Tip-Associated Localization of Cdc42 Is F-Actin Dependent in
Candida albicans
Authors: Hazan Idit , Liu Haoping 
Published: December 2002

ABSTRACT

The rho-type GTPase Cdc42 is important for the establishment and maintenance of eukaryotic cell polarity. To examine whether Cdc42 is regulated during the yeast-to-hypha transition in
Candida albicans
, we constructed a green fluorescence protein (GFP)-Cdc42 fusion under the
ACT1
promoter and observed its localization in live
C. albicans
cells. As in
Saccharomyces cerevisiae
, GFP-Cdc42 was observed around the entire periphery of the cell. In yeast-form cells of
C. albicans
, it clustered to the tips and sides of small buds as well as to the mother-daughter neck region of large-budded cells. Upon hyphal induction, GFP-Cdc42 clustered to the site of hyphal evagination and remained at the tips of the hyphae. This temporal and spatial localization of Cdc42 suggests that its activity is regulated during the yeast-to-hypha transition. In addition to the accumulation at the hyphal tip, GFP-Cdc42 was also seen as a band within the hyphal tube in cells that had undergone nuclear separation. With the F-actin-assembly inhibitor latrunculin A, we found that GFP-Cdc42 accumulation at the bud site in yeast-form cells is F-actin independent, whereas GFP-Cdc42 accumulation at the hyphal tip requires F-actin. Furthermore, disruption of the F-actin cytoskeleton impaired the transcriptional induction of hypha-specific genes. Therefore, hypha formation resembles mating in
Saccharomyces cerevisiae
in that both require F-actin for GFP-Cdc42 localization and efficient signaling.
Gpa2, a G-Protein α Subunit Required for Hyphal Development in
Candida albicans
Authors: Sánchez-Martínez Cristina , Pérez-Martín José 
Published: December 2002

ABSTRACT

Candida albicans
is able to respond to environmental changes by inducing a distinct morphological program, which is related to the ability to infect mammalian hosts. Although some of the signal transduction pathways involved in this response are known, it is not clear how the environmental signals are sensed and transmitted to these transduction cascades. In this work, we have studied the function of
GPA2
, a new gene from
C. albicans
, which encodes a G-protein α-subunit homologue. We demonstrate that Gpa2 plays an important role in the yeast-hypha dimorphic transition in the response of
C. albicans
to some environmental inducers. Deletion of both alleles of the
GPA2
gene causes in vitro defects in morphological transitions in Spider medium and SLAD medium and in embedded conditions but not in medium containing serum. These defects cannot be reversed by exogenous addition of cyclic AMP. However, overexpression of
HST7
, which encodes a component of the filament-inducing mitogen-activated protein kinase (MAPK) cascade, bypasses the Gpa2 requirement. We have obtained different gain-of-function and loss-of-function mutant alleles of the
GPA2
gene, which we have introduced in several
C. albicans
genetic backgrounds. Our results indicate that, in response to environmental cues, Gpa2 is required for the regulation of a MAPK signaling pathway.
Cloning and Characterization ofscon-3+, a New Member of theNeurospora crassaSulfur Regulatory System
Authors: Sizemore Steven T. , Paietta John V. 
Published: December 2002

ABSTRACTThe sulfur regulatory system ofNeurospora crassaconsists of a group of sulfur-regulated structural genes (e.g., arylsulfatase) that are under coordinate control of the CYS3 positive regulator andsulfur controller(SCON) negative regulators. Here we report on the cloning ofscon-3+, which encodes a polypeptide of 171 amino acids and is a Skp1 family homolog. Repeat-induced point mutation ofscon-3+resulted in a phenotype of constitutive expression of arylsulfatase, a phenotype consistent with othersulfur controllermutants. Northern analysis indicated that, unlike other members of the sulfur regulatory system, expression ofscon-3+is not under the direct control of the CYS3 transcriptional activator. In particular,scon-3+mRNA was detectable under sulfur repressing or derepressing conditions in a Δcys-3mutant. In yeast, Skp1p and an F-box protein binding partner are core constituents of a class of E3 ubiquitin ligases known as SCF complexes. TheN. crassanegative regulator SCON2 contains an F-box motif essential for the operation of the sulfur regulatory system and suggests a role for an SCF complex in theN. crassasulfur regulatory system. A crucial set of experiments, by using a yeast two-hybrid approach with confirming coimmunoprecipitation assays, demonstrated that SCON3 interacts with SCON2 in a manner dependent upon the F-box motif of SCON2. The protein-protein interaction detected between SCON2 and SCON3 represents the initial demonstration in a filamentous fungus of functional interaction between putative core components of a SCF complex.
The Glc7p-Interacting Protein Bud14p Attenuates Polarized Growth, Pheromone Response, and Filamentous Growth in
Saccharomyces cerevisiae
Authors: Cullen Paul J. , Sprague George F. 
Published: December 2002

ABSTRACT

A genetic selection in
Saccharomyces cerevisiae
for mutants that stimulate the mating pathway uncovered a mutant that had a hyperactive pheromone response pathway and also had hyperpolarized growth. Cloning and segregation analysis demonstrated that
BUD14
was the affected gene. Disruption of
BUD14
in wild-type cells caused mild stimulation of pheromone response pathway reporters, an increase in sensitivity to mating factor, and a hyperelongated shmoo morphology. The
bud14
mutant also had hyperfilamentous growth. Consistent with a role in the control of cell polarity, a Bud14p-green fluorescent protein fusion was localized to sites of polarized growth in the cell. Bud14p shared morphogenetic functions with the Ste20p and Bni1p proteins as well as with the type 1 phosphatase Glc7p. The genetic interactions between
BUD14
and
GLC7
suggested a role for Glc7p in filamentous growth, and Glc7p was found to have a positive function in filamentous growth in yeast.