bluuebunny/crossref_metadata_2025_split huggingface dataset:
Shared and Independent Roles for a Gα
i
Protein and Adenylyl Cyclase in Regulating Development and Stress Responses in
Neurospora crassa
Authors: Ivey F. Douglas , Kays Ann M. , Borkovich Katherine A. 
Published: December 2002

ABSTRACT

Growth and development are regulated using cyclic AMP (cAMP)-dependent and -independent pathways in
Neurospora crassa
. The
cr-1
adenylyl cyclase mutant lacks detectable cAMP and exhibits numerous defects, including colonial growth habit, short aerial hyphae, premature conidiation on plates, inappropriate conidiation in submerged culture, and increased thermotolerance. Evidence suggests that the heterotrimeric Gα protein GNA-1 is a direct positive regulator of adenylyl cyclase. Δ
gna-1
strains are female-sterile, and Δ
gna-1
strains have reduced apical extension rates on normal and hyperosmotic medium, greater resistance to oxidative and heat stress, and stunted aerial hyphae compared to the wild-type strain. In this study, a Δ
gna-1 cr-1
double mutant was analyzed to differentiate cAMP-dependent and -independent signaling pathways regulated by GNA-1. Δ
gna-1 cr-1
mutants have severely restricted colonial growth and do not produce aerial hyphae on plates or in standing liquid cultures. Addition of cAMP to plates or standing liquid cultures rescues
cr-1
, but not Δ
gna-1 cr-1
, defects, which is consistent with previous results demonstrating that Δ
gna-1
mutants do not respond to exogenous cAMP. The females of all strains carrying the Δ
gna-1
mutation are sterile; however, unlike
cr-1
and Δ
gna-1
strains, the Δ
gna-1 cr-1
mutant does not produce protoperithecia. The Δ
gna-1
and
cr-1
mutations were synergistic with respect to inappropriate conidiation during growth in submerged culture. Thermotolerance followed the order wild type < Δ
gna-1
<
cr-1
= Δ
gna-1 cr-1
, consistent with a cAMP-dependent process. Taken together, the results suggest that in general, GNA-1 and CR-1 regulate
N. crassa
growth and development using parallel pathways, while thermotolerance is largely dependent on cAMP.
Evolutionary Analyses of ABC Transporters of
Dictyostelium discoideum
Authors: Anjard Christophe ,   the Dictyostelium Sequencing Consortium, Loomis William F. 
Published: December 2002

ABSTRACT

The ABC superfamily of genes is one of the largest in the genomes of both bacteria and eukaryotes. The proteins encoded by these genes all carry a characteristic 200- to 250-amino-acid ATP-binding cassette that gives them their family name. In bacteria they are mostly involved in nutrient import, while in eukaryotes many are involved in export. Seven different families have been defined in eukaryotes based on sequence homology, domain topology, and function. While only 6 ABC genes in
Dictyostelium discoideum
have been studied in detail previously, sequences from the well-advanced
Dictyostelium
genome project have allowed us to recognize 68 members of this superfamily. They have been classified and compared to animal, plant, and fungal orthologs in order to gain some insight into the evolution of this superfamily. It appears that many of the genes inferred to have been present in the ancestor of the crown organisms duplicated extensively in some but not all phyla, while others were lost in one lineage or the other.
Synthesis of Chloroplast Galactolipids in Apicomplexan Parasites
Authors: Maréchal Eric , Azzouz Nahid , Santos de Macedo Cristiana , Block Maryse A. , Feagin Jean E. , Schwarz Ralph T. , Joyard Jacques 
Published: December 2002

ABSTRACT

Monogalactosyldiacylglycerol and digalactosyldiacylglycerol are major chloroplast lipids of algae and land plants and are synthesized within the plastid envelope. Here we report that in
Toxoplasma gondii
and
Plasmodium falciparum
lysates, radiolabeled UDP-galactose is incorporated into monogalactosylcerebrosides, monogalactosyldiacylglycerol, and digalactosyldiacylglycerol due to distinct enzymological activities. Furthermore, DGDG is immunologically detected in apicomplexans.
Amino Acid-Dependent Gcn4p Stability Regulation Occurs Exclusively in the Yeast Nucleus
Authors: Pries Ralph , Bömeke Katrin , Irniger Stefan , Grundmann Olav , Braus Gerhard H. 
Published: December 2002

ABSTRACT

The c-Jun-like transcriptional activator Gcn4p controls biosynthesis of translational precursors in the yeast
Saccharomyces cerevisiae
. Protein stability is dependent on amino acid limitation and
cis
signals within Gcn4p which are recognized by cyclin-dependent protein kinases, including Pho85p. The Gcn4p population within unstarved yeast consists of a small relatively stable cytoplasmic fraction and a larger less stable nuclear fraction. Gcn4p contains two nuclear localization signals (NLS) which function independently of the presence or absence of amino acids. Expression of NLS-truncated Gcn4p results in an increased cytoplasmic fraction and an overall stabilization of the protein. The same effect is achieved for the entire Gcn4p in a
yrb1
yeast mutant strain impaired in the nuclear import machinery. In the presence of amino acids, controlled destabilization of Gcn4p is triggered by the phosphorylation activity of Pho85p. A
pho85Δ
mutation stabilizes Gcn4p without affecting nuclear import. Pho85p is localized within the nucleus in the presence or absence of amino acids. Therefore, there is a strict spatial separation of protein synthesis and degradation of Gcn4p in yeast. Control of protein stabilization which antagonizes Gcn4p function is restricted to the nucleus.
Dual Role of the
Saccharomyces cerevisiae
TEA/ATTS Family Transcription Factor Tec1p in Regulation of Gene Expression and Cellular Development
Authors: Köhler Tim , Wesche Stefanie , Taheri Naimeh , Braus Gerhard H. , Mösch Hans-Ulrich 
Published: December 2002

ABSTRACT

In
Saccharomyces cerevisiae
, the transcription factors Tec1p and Ste12p are required for haploid invasive and diploid pseudohyphal growth. Tec1p and Ste12p have been postulated to regulate these developmental processes primarily by cooperative binding to filamentous and invasion-responsive elements (FREs), which are combined enhancer elements that consist of a Tec1p-binding site (TCS) and an Ste12p-binding site (PRE). They are present in the promoter regions of target genes, e.g.,
FLO11
. Here, we show that Tec1p efficiently activates target gene expression and cellular development in the absence of Ste12p. We further demonstrate that TCS elements alone are sufficient to mediate Tec1p-driven gene expression by a mechanism termed TCS control that is operative even when Ste12p is absent. Mutational analysis of
TEC1
revealed that TCS control,
FLO11
expression, and haploid invasive growth require the C terminus of Tec1p. In contrast, the Ste12p-dependent FRE control mechanism is sufficiently executed by the N-terminal portion of Tec1p, which contains the TEA/ATTS DNA-binding domain. Our study suggests that regulation of haploid invasive and diploid pseudohyphal growth by Ste12p and Tec1p is not only executed by combinatorial control but involves additional control mechanisms in which Ste12p activates
TEC1
expression via clustered PREs and where Tec1p regulates expression of target genes, e.g.,
FLO11
, by TCS control.
Novel Protein Kinase Induced during Sporangial Cleavage in the Oomycete
Phytophthora infestans
Authors: Judelson Howard S. , Roberts Samuel 
Published: December 2002

ABSTRACT

A study of the effect of inhibitors on zoospore development in
Phytophthora infestans
demonstrated the involvement of protein kinases and calcium and led to the discovery of a gene induced during zoosporogenesis that encoded a protein resembling Ca
+2
- and calmodulin-regulated serine/threonine protein kinases. The calcium channel blocker verapamil and the calmodulin antagonist trifluoroperazine inhibited zoosporogenesis and encystment. The protein kinase inhibitors K-252a and KN-93 inhibited zoospore release, encystment, and cyst germination, and K-252a reduced zoospore viability. In contrast, the inhibitors had minor or no effects on sporangia directly germinating in media. Spurred by these findings, a survey of putative protein kinase genes was performed to identify any that were up-regulated during zoosporogenesis. A kinase-encoding gene was identified for which mRNA accumulation was first detected soon after chilling sporangia in water, conditions that induce sporangial cytoplasm to cleave and release zoospores. The transcript persisted in motile zoospores and in germinated cysts but was not detected in other tissues, including hyphae, hyphae placed in water, or directly germinating sporangia. The structure of the predicted protein was novel, as its C-terminal region, which binds calmodulin in related proteins, was unusually short. Concentrations of actinomycin D previously used in experiments that suggested that de novo transcription was not needed for zoosporogenesis or encystment only partially inhibited transcription of the kinase gene, probably due to poor uptake into sporangia.
Intracellular Maltose Is Sufficient To Induce
MAL
Gene Expression in
Saccharomyces cerevisiae
Authors: Wang Xin , Bali Mehtap , Medintz Igor , Michels Corinne A. 
Published: December 2002

ABSTRACT

The presence of maltose induces
MAL
gene expression in
Saccharomyces
cells, but little is known about how maltose is sensed. Strains with all maltose permease genes deleted are unable to induce
MAL
gene expression. In this study, we examined the role of maltose permease in maltose sensing by substituting a heterologous transporter for the native maltose permease.
PmSUC2
encodes a sucrose transporter from the dicot plant
Plantago major
that exhibits no significant sequence homology to maltose permease. When expressed in
Saccharomyces cerevisiae
, PmSUC2 is capable of transporting maltose, albeit at a reduced rate. We showed that introduction of
PmSUC2
restores maltose-inducible
MAL
gene expression to a maltose permease-null mutant and that this induction requires the
MAL
activator. These data indicate that intracellular maltose is sufficient to induce
MAL
gene expression independently of the mechanism of maltose transport. By using strains expressing defective
mal61
mutant alleles, we demonstrated a correlation between the rate of maltose transport and the level of the induction, which is particularly evident in medium containing very limiting concentrations of maltose. Moreover, our results indicate that a rather low concentration of intracellular maltose is needed to trigger
MAL
gene expression. We also showed that constitutive overexpression of either
MAL61
maltose permease or
PmSUC2
suppresses the noninducible phenotype of a defective
mal13 MAL
-activator allele, suggesting that this suppression is solely a function of maltose transport activity and is not specific to the sequence of the permease. Our studies indicate that maltose permease does not function as the maltose sensor in
S. cerevisiae
.
Mating-Type Locus of
Cryptococcus neoformans
: a Step in the Evolution of Sex Chromosomes
Authors: Lengeler Klaus B. , Fox Deborah S. , Fraser James A. , Allen Andria , Forrester Keri , Dietrich Fred S. , Heitman Joseph 
Published: December 2002

ABSTRACT

The sexual development and virulence of the fungal pathogen
Cryptococcus neoformans
is controlled by a bipolar mating system determined by a single locus that exists in two alleles, α and
a
. The α and
a
mating-type alleles from two divergent varieties were cloned and sequenced. The
C. neoformans
mating-type locus is unique, spans >100 kb, and contains more than 20 genes.
MAT
-encoded products include homologs of regulators of sexual development in other fungi, pheromone and pheromone receptors, divergent components of a MAP kinase cascade, and other proteins with no obvious function in mating. The α and
a
alleles of the mating-type locus have extensively rearranged during evolution and strain divergence but are stable during genetic crosses and in the population. The
C. neoformans
mating-type locus is strikingly different from the other known fungal mating-type loci, sharing features with the self-incompatibility systems and sex chromosomes of algae, plants, and animals. Our study establishes a new paradigm for mating-type loci in fungi with implications for the evolution of cell identity and self/nonself recognition.
Isocitrate Lyase Is Essential for Pathogenicity of the Fungus
Leptosphaeria maculans
to Canola
(
Brassica napus
)
Authors: Idnurm Alexander , Howlett Barbara J. 
Published: December 2002

ABSTRACT

A pathogenicity gene has been identified in
Leptosphaeria maculans
, the ascomycetous fungus that causes blackleg disease of canola (
Brassica napus)
. This gene encodes isocitrate lyase, a component of the glyoxylate cycle, and is essential for the successful colonization of
B. napus
. It was identified by a reverse genetics approach whereby a plasmid conferring hygromycin resistance was inserted randomly into the
L. maculans
genome. Twelve of 516 transformants tested had reduced pathogenicity on cotyledons of
B. juncea
and
B. napus
, and 1 of these 12 had a deletion of the isocitrate lyase gene, as well as an insertion of the hygromycin resistance gene. This mutant was unable to grow on fatty acids, including monolaurate, and the isocitrate lyase transcript was not detected. When the wild-type gene was reintroduced into the mutant, growth on monolaurate was restored and pathogenicity was partially restored.
L. maculans
isocitrate lyase is produced during infection of
B. napus
cotyledons, while the plant homologue is not. When 2.5% glucose was added to the inoculum of the isocitrate lyase mutant, lesions of sizes similar to those caused by wild-type isolate M1 developed on
B. napus
cotyledons. These findings suggest that the glyoxylate pathway is essential for disease development by this plant-pathogenic fungus, as has been shown recently for a fungal and bacterial pathogen of animals and a bacterial pathogen of plants. Involvement of the glyoxylate pathway in pathogenesis in animals and plants presents potential drug targets for control of diseases.
Aspergillus nidulansCatalase-Peroxidase Gene (cpeA) Is Transcriptionally Induced during Sexual Development through the Transcription Factor StuA
Authors: Scherer Mario , Wei Huijun , Liese Ralf , Fischer Reinhard 
Published: December 2002

ABSTRACTCatalases, peroxidases, and catalase-peroxidases are important enzymes to cope with reactive oxygen species in pro- and eukaryotic cells. In the filamentous fungusAspergillus nidulansthree monofunctional catalases have been described, and a fourth catalase activity was observed in native polyacrylamide gels. The latter activity is probably due to the bifunctional enzyme catalase-peroxidase, which we characterized here. The gene, namedcpeA, encodes an 81-kDa polypeptide with a conserved motif for heme coordination. The enzyme comprises of two similar domains, suggesting gene duplication and fusion during evolution. The first 439 amino acids share 22% identical residues with the C terminus. Homologous proteins are found in several prokaryotes, such asEscherichia coliandMycobacterium tuberculosis(both with 61% identity). In fungi the enzyme has been noted inPenicillium simplicissimum,Septoria tritici, andNeurospora crassa(69% identical amino acids) but is absent fromSaccharomyces cerevisiae.Expression analysis inA. nidulansrevealed that the gene is transcriptionally induced upon carbon starvation and during sexual development, but starvation is not sufficient to reach high levels of the transcript during development. Besides transcriptional activation, we present evidence for posttranscriptional regulation. A green fluorescent protein fusion protein localized to the cytoplasm of Hülle cells. The Hülle cell-specific expression was dependent on the developmental regulator StuA, suggesting an activating function of this helix-loop-helix transcription factor.
Copper-Dependent Iron Assimilation Pathway in the Model Photosynthetic EukaryoteChlamydomonas reinhardtii
Authors: La Fontaine Sharon , Quinn Jeanette M. , Nakamoto Stacie S. , Page M. Dudley , Göhre Vera , Moseley Jeffrey L. , Kropat Janette , Merchant Sabeeha 
Published: December 2002

ABSTRACTThe unicellular green algaChlamydomonas reinhardtiiis a valuable model for studying metal metabolism in a photosynthetic background. A search of theChlamydomonasexpressed sequence tag database led to the identification of several components that form a copper-dependent iron assimilation pathway related to the high-affinity iron uptake pathway defined originally forSaccharomyces cerevisiae. They include a multicopper ferroxidase (encoded byFox1), an iron permease (encoded byFtr1), a copper chaperone (encoded byAtx1), and a copper-transporting ATPase. A cDNA,Fer1, encoding ferritin for iron storage also was identified. Expression analysis demonstrated thatFox1andFtr1were coordinately induced by iron deficiency, as wereAtx1andFer1, although to lesser extents. In addition, Fox1 abundance was regulated at the posttranscriptional level by copper availability. Each component exhibited sequence relationship with its yeast, mammalian, or plant counterparts to various degrees; Atx1 ofC. reinhardtiiis also functionally related with respect to copper chaperone and antioxidant activities. Fox1 is most highly related to the mammalian homologues hephaestin and ceruloplasmin; its occurrence and pattern of expression inChlamydomonasindicate, for the first time, a role for copper in iron assimilation in a photosynthetic species. Nevertheless, growth ofC. reinhardtiiunder copper- and iron-limiting conditions showed that, unlike the situation in yeast and mammals, where copper deficiency results in a secondary iron deficiency, copper-deficientChlamydomonascells do not exhibit symptoms of iron deficiency. We propose the existence of a copper-independent iron assimilation pathway in this organism.
mcl1
+

, the
Schizosaccharomyces pombe
Homologue of
CTF4
, Is Important for Chromosome Replication, Cohesion, and Segregation
Authors: Williams Dewight R. , McIntosh J. Richard 
Published: December 2002

ABSTRACT

The fission yeast minichromosome loss mutant
mcl1-1
was identified in a screen for mutants defective in chromosome segregation. Missegregation of the chromosomes in
mcl1-1
mutant cells results from decreased centromeric cohesion between sister chromatids.

mcl1
+

encodes a β-transducin-like protein with similarity to a family of eukaryotic proteins that includes Ctf4p from
Saccharomyces cerevisiae
, sepB from
Aspergillus nidulans
, and AND-1 from humans. The previously identified fungal members of this protein family also have chromosome segregation defects, but they primarily affect DNA metabolism. Chromosomes from
mcl1-1
cells were heterogeneous in size or structure on pulsed-field electrophoresis gels and had elongated heterogeneous telomeres.
mcl1-1
was lethal in combination with the DNA checkpoint mutations
rad3Δ
and
rad26Δ
, demonstrating that loss of Mcl1p function leads to DNA damage.
mcl1-1
showed an acute sensitivity to DNA damage that affects S-phase progression. It interacts genetically with replication components and causes an S-phase delay when overexpressed. We propose that Mcl1p, like Ctf4p, has a role in regulating DNA replication complexes.
Eng1p, an Endo-1,3-β-Glucanase Localized at the Daughter Side of the Septum, Is Involved in Cell Separation in
Saccharomyces cerevisiae
Authors: Baladrón Victoriano , Ufano Sandra , Dueñas Encarnación , Martín-Cuadrado Ana Belén , del Rey Francisco , Vázquez de Aldana Carlos R. 
Published: December 2002

ABSTRACT

ENG1
(
YNR067c
), a gene encoding a new endo-1,3-β-glucanase, was cloned by screening a genomic library with a DNA probe obtained by PCR with synthetic oligonucleotides designed according to conserved regions found between yeast exo-1,3-β-glucanases (Exg1p, Exg2p, and Ssg1p). Eng1p shows strong sequence similarity to the product of the
Saccharomyces cerevisiae ACF2
gene, involved in actin assembly “in vitro,” and to proteins present in other yeast and fungal species. It is also related to plant glucan-binding elicitor proteins, which trigger the onset of a defense response upon fungal infection. Eng1p and Acf2p/Eng2p are glucan-hydrolyzing proteins that specifically act on 1,3-β linkages, with an endolytic mode of action. Eng1p is an extracellular, heavily glycosylated protein, while Acf2p/Eng2p is an intracellular protein with no carbohydrate linked by N-glycosidic bonds.
ENG1
transcription fluctuates periodically during the cell cycle; maximal accumulation occurs during the M/G
1
transition and is dependent on the transcription factor Ace2p. Interestingly,
eng1
deletion mutants show defects in cell separation, and Eng1p localizes asymmetrically to the daughter side of the septum, suggesting that this protein is involved, together with chitinase, in the dissolution of the mother-daughter septum.
A Forkhead Transcription Factor Is Important for True Hyphal as well as Yeast Morphogenesis in
Candida albicans
Authors: Bensen Eric S. , Filler Scott G. , Berman Judith 
Published: December 2002

ABSTRACT

Candida albicans
is an important pathogen of immunocompromised patients which grows with true hyphal, pseudohyphal, and yeast morphologies. The dynamics of cell cycle progression are markedly different in true hyphal relative to pseudohyphal and yeast cells, including nuclear movement and septin ring positioning. In
Saccharomyces cerevisiae
, two forkhead transcription factors (
ScFKH1
and
ScFKH2
) regulate the expression of B-cyclin genes. In both
S. cerevisiae
and
Schizosaccharomyces pombe
, forkhead transcription factors also influence morphogenesis. To explore the molecular mechanisms that connect
C. albicans
morphogenesis with cell cycle progression, we analyzed
CaFKH2
, the single homolog of
S. cerevisiae FKH1/FKH2. C. albicans
cells lacking CaFkh2p formed constitutive pseudohyphae under all yeast and hyphal growth conditions tested. Under hyphal growth conditions levels of hyphae-specific mRNAs were reduced, and under yeast growth conditions levels of several genes encoding proteins likely to be important for cell wall separation were reduced. Together these results imply that Fkh2p is required for the morphogenesis of true hyphal as well as yeast cells. Efg1p and Cph1p, two transcription factors that contribute to
C. albicans
hyphal growth, were not required for the pseudohyphal morphology of
fkh2
mutants, implying that Fkh2p acts in pathways downstream of and/or parallel to Efg1p and Cph1p. In addition, cells lacking Fkh2p were unable to damage human epithelial or endothelial cells in vitro, suggesting that Fkh2p contributes to
C. albicans
virulence.