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1.
G3 (Bethesda) ; 7(4): 1149-1155, 2017 04 03.
Article in English | MEDLINE | ID: mdl-28179391

ABSTRACT

In the filamentous fungus Neurospora crassa, cross walls between individual cells are normally incomplete, making the entire fungal network vulnerable to attack by viruses and selfish DNAs. Accordingly, several genome surveillance mechanisms are maintained to help the fungus combat these repetitive elements. One of these defense mechanisms is called meiotic silencing by unpaired DNA (MSUD), which identifies and silences unpaired genes during meiosis. Utilizing common RNA interference (RNAi) proteins, such as Dicer and Argonaute, MSUD targets mRNAs homologous to the unpaired sequence to achieve silencing. In this study, we have identified an additional silencing component, namely the cap-binding complex (CBC). Made up of cap-binding proteins CBP20 and CBP80, CBC associates with the 5' cap of mRNA transcripts in eukaryotes. The loss of CBC leads to a deficiency in MSUD activity, suggesting its role in mediating silencing. As confirmed in this study, CBC is predominantly nuclear, although it is known to travel in and out of the nucleus to facilitate RNA transport. As seen in animals but not in plants, CBP20's robust nuclear import depends on CBP80 in Neurospora CBC interacts with a component (Argonaute) of the perinuclear meiotic silencing complex (MSC), directly linking the two cellular factors.


Subject(s)
DNA, Fungal/metabolism , Gene Silencing , Meiosis , Neurospora/cytology , Neurospora/genetics , Nuclear Cap-Binding Protein Complex/metabolism , Cell Nucleus/metabolism , DNA, Fungal/genetics , Genes, Fungal , Protein Binding
2.
J Theor Biol ; 387: 206-13, 2015 Dec 21.
Article in English | MEDLINE | ID: mdl-26463679

ABSTRACT

The problem of phase synchronization for a population of genetic oscillators (circadian clocks, synthetic oscillators, etc.) is considered in this paper, taking into account a cell division process and a common entrainment input in the population. The proposed analysis approach is based on the Phase Response Curve (PRC) model of an oscillator (the first order reduced model obtained for the linearized system and inputs with infinitesimal amplitude). The occurrence of cell division introduces state resetting in the model, placing it in the class of hybrid systems. It is shown that without common entraining input in all oscillators, the cell division acts as a disturbance causing phase drift, while the presence of entrainment guarantees boundedness of synchronization phase errors in the population. The performance of the obtained solutions is demonstrated via computer experiments for two different models of circadian/genetic oscillators (Neurospora׳s circadian oscillation model and the repressilator).


Subject(s)
Cell Division , Circadian Rhythm/physiology , Neurospora/cytology , Neurospora/physiology , Models, Biological
3.
Dev Cell ; 34(4): 410-20, 2015 Aug 24.
Article in English | MEDLINE | ID: mdl-26305593

ABSTRACT

Cytoplasmic streaming occurs in diverse cell types, where it generally serves a transport function. Here, we examine streaming in multicellular fungal hyphae and identify an additional function wherein regimented streaming forms distinct cytoplasmic subcompartments. In the hypha, cytoplasm flows directionally from cell to cell through septal pores. Using live-cell imaging and computer simulations, we identify a flow pattern that produces vortices (eddies) on the upstream side of the septum. Nuclei can be immobilized in these microfluidic eddies, where they form multinucleate aggregates and accumulate foci of the HDA-2 histone deacetylase-associated factor, SPA-19. Pores experiencing flow degenerate in the absence of SPA-19, suggesting that eddy-trapped nuclei function to reinforce the septum. Together, our data show that eddies comprise a subcellular niche favoring nuclear differentiation and that subcompartments can be self-organized as a consequence of regimented cytoplasmic streaming.


Subject(s)
Cell Compartmentation , Cytoplasmic Streaming , Cell Differentiation , Cell Nucleus/metabolism , Cell Wall/metabolism , Genes, Fungal , Hyphae/cytology , Hyphae/growth & development , Microtubules/metabolism , Mutation , Neurospora/cytology , Neurospora/genetics , Neurospora/physiology , Rheology , Stress, Mechanical , Subcellular Fractions/metabolism
4.
J Evol Biol ; 27(6): 1125-35, 2014 Jun.
Article in English | MEDLINE | ID: mdl-24848562

ABSTRACT

Mounting evidence indicates that changes in the transcriptome contribute significantly to the phenotypic differentiation of closely related species. Nonetheless, further genome-wide studies, spanning a broad range of organisms, are needed to decipher the factors driving transcriptome evolution. The model Neurospora (Ascomycota) comprises a simple system for empirically studying the evolutionary dynamics of the transcriptome. Here, we studied the evolution of gene expression in Neurospora crassa and Neurospora tetrasperma and show that patterns of transcriptome evolution are connected to genome evolution, tissue type and sexual identity (mating types, mat A and mat a) in these eukaryotes. Based on the comparisons of inter- and intraspecies expression divergence, our data reveal that rapid expression divergence is more apt to occur in sexual/female (SF) than vegetative/male (VM) tissues. In addition, interspecies gene expression and protein sequence divergence were strongly correlated for SF, but not VM, tissue. A correlation between transcriptome and protein evolution parallels findings from certain animals, but not yeast, and add support for the theory that expression evolution differs fundamentally among multicellular and unicellular eukaryotes. Finally, we found that sexual identity in these hermaphroditic Neurospora species is connected to interspecies expression divergence in a tissue-dependent manner: rapid divergence occurred for mat A- and mat a-biased genes from SF and VM tissues, respectively. Based on these findings, it is hypothesized that rapid interspecies transcriptome evolution is shifting the mating types of Neurospora towards distinct female and male phenotypes, that is, sexual dimorphism.


Subject(s)
Evolution, Molecular , Neurospora/genetics , Transcriptome , Gene Expression Profiling , Genome, Fungal , Molecular Sequence Data , Neurospora/cytology , Phenotype , Reproduction
5.
Dev Cell ; 21(3): 457-68, 2011 Sep 13.
Article in English | MEDLINE | ID: mdl-21920312

ABSTRACT

A fundamental question in cell biology is how cells control organelle composition and abundance. Woronin bodies are fungal peroxisomes centered on a crystalline core of the self-assembled HEX protein. Despite using the canonical peroxisome import machinery for biogenesis, Woronin bodies are scarce compared to the overall peroxisome population. Here, we show that HEX oligomers promote the differentiation of a subpopulation of peroxisomes, which become enlarged and highly active in matrix protein import. HEX physically associates with the essential matrix import peroxin, PEX26, and promotes its enrichment in the membrane of differentiated peroxisomes. In addition, a PEX26 mutant that disrupts differentiation produces increased numbers of aberrantly small Woronin bodies. Our data suggest a mechanism where HEX oligomers recruit a key component of the import machinery, which promotes the import of additional HEX. This type of positive feedback provides a basic mechanism for the production of an organelle subpopulation of distinct composition and abundance.


Subject(s)
Feedback, Physiological , Fungal Proteins/metabolism , Neurospora/cytology , Peroxisomes/metabolism , Polymers/metabolism , Cell Differentiation , Fungal Proteins/chemistry , Membrane Proteins/chemistry , Membrane Proteins/metabolism , Protein Binding , Protein Transport
6.
Mol Biol Cell ; 19(11): 4554-69, 2008 Nov.
Article in English | MEDLINE | ID: mdl-18716060

ABSTRACT

Regulation of Rho GTPase signaling is critical for cell shape determination and polarity. Here, we investigated the role of LRG1, a novel member of the GTPase-activating proteins (GAPs) of Neurospora crassa. LRG1 is essential for apical tip extension and to restrict excessive branch formation in subapical regions of the hypha and is involved in determining the size of the hyphal compartments. LRG1 localizes to hyphal tips and sites of septation via its three LIM domains. The accumulation of LRG1 as an apical cap is dependent on a functional actin cytoskeleton and active growth, and is influenced by the opposing microtubule-dependent motor proteins dynein and kinesin-1. Genetic evidence and in vitro GTPase assays identify LRG1 as a RHO1-specific GAP affecting several output pathways of RHO1, based on hyposensitivity to the glucan inhibitor caspofungin, synthetic lethality with a hyperactive beta1,3-glucan synthase mutant, altered PKC/MAK1 pathway activities, and hypersensitivity to latrunculin A. The morphological defects of lrg-1 are highly reminiscent to the Ndr kinase/RAM pathway mutants cot-1 and pod-6, and genetic evidence suggests that RHO1/LRG1 function in parallel with COT1 in coordinating apical tip growth.


Subject(s)
Cell Polarity , Fungal Proteins/metabolism , GTPase-Activating Proteins/metabolism , Neurospora/enzymology , Neurospora/growth & development , Signal Transduction , rho GTP-Binding Proteins/metabolism , Fungal Proteins/chemistry , Hyphae/growth & development , Microtubules/metabolism , Models, Biological , Molecular Motor Proteins/metabolism , Mutation/genetics , Neurospora/cytology , Protein Structure, Tertiary , Protein Transport
7.
FEBS Lett ; 581(30): 5759-64, 2007 Dec 22.
Article in English | MEDLINE | ID: mdl-18037381

ABSTRACT

The large (l) and small (s) isoforms of FREQUENCY (FRQ) are elements of interconnected feedback loops of the Neurospora circadian clock. The expression ratio of l-FRQ vs. s-FRQ is regulated by thermosensitive splicing of an intron containing the initiation codon for l-FRQ. We show that this splicing is dependent on light and temperature and displays a circadian rhythm. Strains expressing only l-FRQ or s-FRQ support short and long temperature-compensated circadian rhythms, respectively. The thermosensitive expression ratio of FRQ isoforms influences period length in wt. Our data indicate that differential expression of FRQ isoforms is not required for temperature compensation but rather provides a means to fine-tune period length in response to ambient temperature.


Subject(s)
Circadian Rhythm/physiology , Fungal Proteins/metabolism , Neurospora/physiology , Temperature , Trans-Activators/metabolism , Alternative Splicing/genetics , Alternative Splicing/radiation effects , Amino Acid Sequence , Base Sequence , CLOCK Proteins , Circadian Rhythm/radiation effects , Fungal Proteins/chemistry , Fungal Proteins/genetics , Light , Molecular Sequence Data , Mutation/genetics , Neurospora/cytology , Neurospora/radiation effects , Protein Isoforms/chemistry , Protein Isoforms/genetics , Protein Isoforms/metabolism , Time Factors , Trans-Activators/chemistry , Trans-Activators/genetics
8.
Genetics ; 176(1): 43-52, 2007 May.
Article in English | MEDLINE | ID: mdl-17339226

ABSTRACT

In Neurospora crassa, pairing of homologous DNA segments is monitored during meiotic prophase I. Any genes not paired with a homolog, as well as any paired homologs of that gene, are silenced during the sexual phase by a mechanism known as meiotic silencing by unpaired DNA (MSUD). Two genes required for MSUD have been described previously: sad-1 (suppressor of ascus dominance), encoding an RNA-directed RNA polymerase, and sad-2, encoding a protein that controls the perinuclear localization of SAD-1. Inactivation of either sad-1 or sad-2 suppresses MSUD. We have now shown that MSUD is also suppressed by either of two Spore killer strains, Sk-2 and Sk-3. These were both known to contain a haplotype segment that behaves as a meiotic drive element in heterozygous crosses of killer x sensitive. Progeny ascospores not carrying the killer element fail to mature and are inviable. Crosses homozygous for either of the killer haplotypes suppress MSUD even though ascospores are not killed. The killer activity maps to the same 30-unit-long region within which recombination is suppressed in killer x sensitive crosses. We suggest that the region contains a suppressor of MSUD.


Subject(s)
Chromosome Pairing/genetics , DNA, Fungal/genetics , Gene Silencing , Meiosis/genetics , Neurospora/genetics , Regulatory Sequences, Nucleic Acid , Spores, Fungal/genetics , Diploidy , Genes, Fungal , Genetic Linkage , Green Fluorescent Proteins/metabolism , Heterozygote , Histones/metabolism , Neurospora/cytology , Recombinant Fusion Proteins/metabolism , Spores, Fungal/cytology , Suppression, Genetic , Tubulin/metabolism
9.
Genetics ; 175(2): 527-44, 2007 Feb.
Article in English | MEDLINE | ID: mdl-17322355

ABSTRACT

New mutations are found among approximately 20% of progeny when one or both parents carry eas allele UCLA191 (eas(UCLA), easily wettable, hydrophobin-deficient, linkage group II). The mutations inactivate the wild-type allele of cya-8 (cytochrome aa3 deficient, linkage group VII), resulting in thin, "transparent" mycelial growth. Other eas alleles fail to produce cya-8 mutant progeny. The recurrent cya-8 mutations are attributed to repeat-induced point mutation (RIP) resulting from a duplicated copy of cya-8+ that was inserted ectopically at eas when the UCLA191 mutation occurred. As expected for RIP, eas(UCLA)-induced cya-8 mutations occur during nuclear proliferation prior to karyogamy. When only one parent is eas(UCLA), the new mutations arise exclusively in eas(UCLA) nuclei. Mutation of cya-8 is suppressed when a long unlinked duplication is present. Stable cya-8 mutations are effectively eliminated in crosses homozygous for rid, a recessive suppressor of RIP. The eas(UCLA) allele is associated with a long paracentric inversion. A discontinuity is present in eas(UCLA) DNA. The eas promoter is methylated in cya-8 progeny of eas(UCLA), presumably by the spreading of methylation beyond the adjoining RIP-inactivated duplication. These findings support a model in which an ectopic insertion that created a mutation at the target site acts as a locus-specific mutator via RIP.


Subject(s)
Mutagenesis, Insertional , Neurospora/genetics , Point Mutation/genetics , Alleles , Cell Nucleus/metabolism , Chromosome Mapping , Crosses, Genetic , Crossing Over, Genetic , DNA, Fungal , Fertilization , Gene Duplication , Gene Silencing , Genes, Fungal , Genetic Linkage , Heterozygote , Homozygote , Meiosis , Models, Genetic , Neurospora/cytology , Neurospora/isolation & purification , Phenotype , Spores, Fungal/genetics , Suppression, Genetic
10.
FEMS Microbiol Lett ; 249(2): 191-8, 2005 Aug 15.
Article in English | MEDLINE | ID: mdl-16040203

ABSTRACT

Conidial anastomosis tubes (CATs) can be recognized in 73 species of filamentous fungi covering 21 genera, and develop in culture and in host-pathogen systems. They have been shown to be morphologically and physiologically distinct from germ tubes in Colletotrichum and Neurospora, and under separate genetic control in Neurospora. CATs are short, thin, usually unbranched and arise from conidia or germ tubes. Their formation is conidium-density dependent, and CATs grow towards each other. MAP kinase mutants of Neurospora are blocked in CAT induction. Nuclei pass through fused CATs and are potential agents of gene exchange between individuals of the same and different species. CAT fusion may also serve to improve the chances of colony establishment.


Subject(s)
Colletotrichum/cytology , Colletotrichum/physiology , Neurospora/cytology , Neurospora/physiology , Cell Fusion , Colletotrichum/ultrastructure , Microscopy, Confocal , Neurospora/ultrastructure
11.
Fungal Genet Biol ; 34(2): 123-9, 2001 Nov.
Article in English | MEDLINE | ID: mdl-11686677

ABSTRACT

Neurospora tetrasperma is naturally heterokaryotic, with cells possessing haploid nuclei of both a and A mating types. As a result, isolates are self-fertile (pseudohomothallic). Occasional homokaryotic ascospores and conidia arise, however, and they produce strains that are self-sterile and must outcross to complete sexual reproduction. Invariably, laboratory crosses employing sibling a and A strains from the same parental heterokaryon restore the pseudohomothallic, heterokaryotic state. In contrast, outcrosses employing a and A strains from different wild isolates typically result in sexual dysfunction. Diverse sexual dysfunction types have been observed, ranging from complete sterility to reduced viability. We report that one type of dysfunction, characterized by spontaneous loss of the heterokaryotic state upon ascospore germination, can result from the interaction of incompatible alleles at heterokaryon incompatibility loci. Specifically, we demonstrate that homoallelism at the het-c locus in N. tetrasperma is required for heterokaryon stability. Heterokaryon incompatibility therefore provides an obstacle to outcrossing in this species, an observation with important implications for fungal life-cycle evolution.


Subject(s)
Alleles , Fungal Proteins/genetics , Neurospora/genetics , Neurospora/physiology , Reproduction/genetics , Crosses, Genetic , Fungal Proteins/metabolism , Genetic Variation/genetics , Haploidy , Neurospora/cytology
12.
Nat Cell Biol ; 2(6): 333-8, 2000 Jun.
Article in English | MEDLINE | ID: mdl-10854323

ABSTRACT

Here, using a quantitative in vivo assay, we map three regions in the carboxy terminus of conventional kinesin that are involved in cargo association, folding and regulation, respectively. Using C-terminal and internal deletions, point mutations, localization studies, and an engineered 'minimal' kinesin, we identify five heptads of a coiled-coil domain in the kinesin tail that are necessary and sufficient for cargo association. Mutational analysis and in vitro ATPase assays highlight a conserved motif in the globular tail that is involved in regulation of the motor domain; a region preceding this motif participates in folding. Although these sites are spatially and functionally distinct, they probably cooperate during activation of the motor for cargo transport.


Subject(s)
Fungal Proteins/chemistry , Fungal Proteins/metabolism , Kinesins/chemistry , Kinesins/metabolism , Neurospora/enzymology , Adenosine Triphosphatases/chemistry , Adenosine Triphosphatases/genetics , Adenosine Triphosphatases/metabolism , Amino Acid Motifs , Amino Acid Sequence , Amino Acid Substitution/genetics , Binding Sites , Conserved Sequence/genetics , Fluorescent Antibody Technique , Fungal Proteins/genetics , Genetic Complementation Test , Kinesins/genetics , Kinetics , Molecular Motor Proteins/chemistry , Molecular Motor Proteins/genetics , Molecular Motor Proteins/metabolism , Molecular Sequence Data , Mutation , Neurospora/cytology , Neurospora/metabolism , Phenotype , Protein Folding , Protein Structure, Tertiary , Recombinant Fusion Proteins/chemistry , Recombinant Fusion Proteins/genetics , Recombinant Fusion Proteins/metabolism , Substrate Specificity
13.
Curr Opin Microbiol ; 3(2): 189-96, 2000 Apr.
Article in English | MEDLINE | ID: mdl-10744993

ABSTRACT

Common regulatory patterns have emerged among the feedback loops lying within circadian systems. Significant progress in dissecting the mechanism of clock resetting by temperature and the role of the WC proteins in the Neurospora light response has accompanied documentation of the importance of nuclear localization and phosphorylation-induced turnover of FRQ to this circadian cycle. The long-awaited molecular description of a transcription/translation loop in the Synechococcus circadian system represents a quantal step forward, followed by the identification of additional important proteins and interactions. Finally, the adaptive significance of rhythms in Synechococcus and by extension in all clocks nicely ties up an extraordinary year.


Subject(s)
Biological Clocks/physiology , Circadian Rhythm/physiology , Cyanobacteria/physiology , Models, Biological , Neurospora/physiology , Biological Clocks/genetics , Circadian Rhythm/genetics , Cyanobacteria/cytology , Cyanobacteria/genetics , Environment , Evolution, Molecular , Genes, Bacterial , Genes, Fungal , Neurospora/cytology , Neurospora/genetics
14.
Trends Cell Biol ; 8(6): 224-30, 1998 Jun.
Article in English | MEDLINE | ID: mdl-9695846

ABSTRACT

Many physiological phenomena are rhythmic and coincide with a particular time of day. These 'circadian rhythms' are not dependent on external timing cues but are driven by internal circadian clocks that are ubiquitous features of living organisms. Although many of these rhythms manifest themselves as complex behavioural patterns, we now know that a circadian clock does not require a complex organism or an elaborate nervous system; it can be built from molecules within an individual cell. This review focuses on new advances in identifying and understanding the basic properties of cellular circadian clocks.


Subject(s)
Circadian Rhythm/physiology , Neurospora/cytology , Neurospora/physiology , Animals , Drosophila/physiology , Photoreceptor Cells, Invertebrate/cytology , Photoreceptor Cells, Invertebrate/physiology , Time Factors
16.
Ann N Y Acad Sci ; 782: 391-401, 1996 May 15.
Article in English | MEDLINE | ID: mdl-8659911

ABSTRACT

Whereas the gene stability related considerations are important in bioprocessing with recombinant cultures, bioreactor design and scale-up require attention to the often reduced shear tolerance of the genetically altered biocatalysts relative to the corresponding wild strains. In addition, the peculiarities of expression of the rDNA product impact the downstream recovery methods. As a consequence, a bioprocessing scheme and the process machinery designed for a naturally occurring organism may need significant modifications for use with a genetically modified variety of the same organism. The case studies described highlight some of the processing constraints and consideration of general relevance.


Subject(s)
Biotechnology/methods , Culture Techniques/methods , Erythrocytes/cytology , Neurospora/growth & development , Recombinant Proteins/biosynthesis , Saccharomyces cerevisiae/growth & development , beta-Galactosidase/biosynthesis , Animals , Cell Survival , Cloning, Molecular/methods , Escherichia coli/enzymology , Hemolysis , Kinetics , Neurospora/cytology , Swine
17.
Can J Genet Cytol ; 28(6): 971-81, 1986 Dec.
Article in English | MEDLINE | ID: mdl-2950988

ABSTRACT

Use of a centromere-linked Spore killer gene Sk reduces manyfold the labor involved in obtaining tetrad data that would otherwise require ordered dissection of intact linear eight-spored asci. Heterozygous crosses are made for Spore killer (SkK X SkS) and for markers to be tested. In such crosses only SkK ascospores survive. The four viable (SkK) and four aborted (SkS) ascospores of each ascus are ejected from the perithecium as a physically disordered group. The four surviving SkK ascospores of individual asci are germinated and scored. SkK segregates from SkS at the first meiotic division. If both marker alleles are represented in the surviving products, they must therefore have segregated from one another at the second division. Four-spore (Fsp) genes have been used to eliminate one postmeiotic nuclear division, so that only two ascospores per ascus need to be scored. The Spore killer method has been useful for mapping closely linked genes in centromere regions, for identifying genes that are far out on chromosome arms, for obtaining information on meiotic crossing-over, and for comparing linkages in different species.


Subject(s)
Centromere/ultrastructure , Chromosomes/ultrastructure , Neurospora/genetics , Cell Division , Genes, Fungal , Genetic Linkage , Meiosis , Neurospora/cytology , Neurospora crassa/genetics , Spores, Fungal/cytology
18.
J Bacteriol ; 154(3): 1397-402, 1983 Jun.
Article in English | MEDLINE | ID: mdl-6304014

ABSTRACT

The divalent cation ionophore A23187 was found to induce apical branching in Neurospora crassa. Optimal effects were obtained by treatment with 0.1 mM ionophore for 30 min. Branching first became manifest during or shortly after treatment; successive rounds of branching could be observed at later times. Calcium starvation of the mycelium markedly reduced its subsequent response to the ionophore, whereas starvation for other divalent cations had no detectable effect. The branching response was markedly reduced in the presence of 10 to 30 mM cyclic AMP or derivatives thereof.


Subject(s)
Calcium/physiology , Neurospora crassa/cytology , Neurospora/cytology , Bucladesine/analogs & derivatives , Bucladesine/pharmacology , Calcimycin/pharmacology , Cyclic AMP/pharmacology , Dose-Response Relationship, Drug , Magnesium/pharmacology , Manganese/pharmacology , Neurospora crassa/physiology , Theophylline/pharmacology
19.
J Cell Sci ; 61: 263-72, 1983 May.
Article in English | MEDLINE | ID: mdl-6224804

ABSTRACT

The correlation between protein synthesis and the nuclear division cycle in Neurospora crassa hyphae was studied by inhibiting protein accumulation by two different experimental procedures: (1) starvation for lysine in a lysine-requiring mutant (lys-1); and (2) addition of cycloheximide. Lysine starvation in a lys-1 strain of N. crassa quickly blocked the nuclear division cycle and nuclei accumulated in G1 phase, as judged by their DNA content. After re-addition of lysine to starved cultures, a discontinuous pattern of uridine incorporation into DNA can be seen, showing that the nuclei were well synchronized. On the other hand, treatment with cycloheximide caused the arrest of a large proportion of the nuclei, also, in the G2 phase of the cell cycle. These results indicate that inhibition of protein synthesis may have multiple effects on the cell cycle in N. crassa and that, while moderate inhibition specifically blocks nuclei at a regulatory point in late G1, strong or complete inhibition demonstrates requirement for protein synthesis at other points in the cycle that are not necessarily regulatory points.


Subject(s)
Cell Nucleus/physiology , Neurospora crassa/cytology , Neurospora/cytology , Plant Proteins/biosynthesis , Cell Division/drug effects , Cell Nucleus/drug effects , Cell Nucleus/metabolism , Cycloheximide/pharmacology , DNA/biosynthesis , Depression, Chemical , Interphase , Lysine/metabolism , Neurospora crassa/metabolism
20.
J Cell Sci ; 48: 127-36, 1981 Apr.
Article in English | MEDLINE | ID: mdl-6456271

ABSTRACT

The timing of the nuclear division cycle in Neurospora crassa was studied by inhibiting DNA synthesis with hydroxyurea added to exponentially growing cultures at concentrations that do not inhibit cytoplasmic growth. After the addition of hydroxyurea only the nuclei that have passed the S-phase divide, and therefore by counting the increase in the average number of nuclei per hypha, the stage in the cycle in which completion of S phase occurred was determined in different nutritional conditions of exponential growth. The stage at which DNA replication terminates is different in different conditions of exponential growth; however, when the length of G2+M phases is calculated a constancy of these phases is shown. Our data indicate that in N. crassa the coordination between cytoplasmic growth and the nuclear division cycle is achieved mainly through a growth-rate-dependent expansion of the G1 phase, according to a sizer-plus-timer model of control of the nuclear division cycle.


Subject(s)
Neurospora crassa/cytology , Neurospora/cytology , Cell Cycle/drug effects , Cell Nucleus/drug effects , Cell Nucleus/metabolism , DNA, Fungal/biosynthesis , Hydroxyurea/pharmacology , Neurospora crassa/drug effects , Time Factors
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