Mutants Of Neurospora Research Articles

Nonlinear Asci without Apical Pores in the Peak Mutant of Neurospora

Previous workers have shown that asci of the Neurospora crassa morphological mutant peak are swollen, and that ascospores are not linearly ordered. In the swollen asci, spindle orientations are abnormal at all three divisions but other events of meiosis and ascospore formation are apparently normal. In the present study, cytological features of ascus development in crosses involving peak are reported in greater detail. The swollen peak asci fail to differentiate apical pores, and mature ascospores are not discharged from the perithecia. The rare linear peak asci form normal apical pores, however. Ascus morphology is described in crosses of peak and two other dominant ascus mutants.

Biology: A Hypothetico-Deductive Science

Ralph W. Lewis Ralph W. Lewis is professor emeritus at Michigan State University, Department of Natural Sciences, East Lansing, MI 48824-1031 where he taught botany, plant pathology, biology and natural science from 1937-1980. He earned his Ph.D. at Michigan State and was a resident fellow at California Tech in 1948. In 1958, Lewis studied at the Instituto Superior di Sanita in Rome. He has done research on fungus nutrition, succinic-less mutants of Neurospora, infection of rye with ergot fungus and a method of large volume spore production by this fungus. Lewis has written papers on the structure of knowledge and its potential for improving education. He believes that through continued work, science education can be largely converted from rote exercises into intellectually active leaming once teachers leam the logical structure of their science and put it to work in their teaching.

A new mutagen-sensitive mutant in Neurospora, mus-16

A new gene, mus-16, is determined by the nitrogen mustard-sensitive Neurospora mutant of Baker, Parish and Curtis (1984) which is defective in the removal of DNA-DNA and DNA-protein crosslinks. This gene is on the left arm of linkage group V between caf-1 and lys-1. The mus-16(JMB) mutant is sensitive to the alkylating agents methyl methanesulfonate (MMS) [dose reduction factor (drf) 8–10 ×], N-methyl- N′-nitro- N-nitrosoguanidine (drf 5–6 ×), the amino acid histidine and the drug hydroxyurea. It is not sensitive to ultraviolet-light, γ-irradiation, or mitomycin C (MMC). It shows normal spontaneous mutation rates but increased induction of mutation by MMS. Homozygous crosses are barren, showing no signs of sporulation. Mitotic spontaneous chromosome instability is increased. The mus-6 mutation is similar to several non-excision repair-defective mutants in Neurospora. Some of these may be defective in repair of alkylation damage. The MMC data supports earlier data that in fungi MMC is incapable of forming DNA-DNA crosslinks.

Blue light induces circadian rhythms in the bd mutant of Neurospora: Double mutants bd,wc-1 and bd,wc-2 are blind

This paper describes a new blue light effect for Neurospora crassa, the photoinduction of circadian rhythms in the bd mutant. The wc-1 and wc-2 genes are necessary for this effect.

Cyclic AMP-dependent, constitutive thermotolerance in the adenylate cyclase-deficient cr-1 (crisp) mutant of Neurospora crassa.

We investigated the heat shock response of the adenylate cyclase deficient mutant cr-1 (crisp) of Neurospora crassa. This strain was observed to be much more resistant to a lethal temperature of 50 degrees C than the wild type. This constitutive thermotolerance was absent in cr-1 conidiospores raised on cyclic AMP (cAMP, 2.5 mM) supplemented solid medium, but was partially restored when the conidiospores were germinated at 30 degrees C, a temperature which fails to induce thermotolerance in the wild-type strain. Two other crisp-like Neurospora mutants, cr-2 and cr-3 which, in contrast to cr-1, contain normal levels of cAMP, did not exhibit the thermotolerance phenomenon observed for cr-1. A cr-1, pe, fl (crisp-microconidial) strain also lacked the ability to tolerate a lethal heat treatment. Our results demonstrate that the adenylate cyclase deficient cr-1 mutant of Neurospora crassa expresses a constitutive thermotolerant phenotype as a consequence of its primary genetic defect: low levels of cAMP.

New supplements for the formate mutant of Neurospora. A possible role for ascorbic acid?

New supplements for the formate mutant of Neurospora. A possible role for ascorbic acid?

A Neurospora Mutant with Abnormal Croziers, Giant Ascospores, and Asci Having Multiple Apical Pores

A Neurospora Mutant with Abnormal Croziers, Giant Ascospores, and Asci Having Multiple Apical Pores

Sorbose-resistant mutants ofNeurospora crassa do not have alteredβ(1–3)glucan synthase activity

A number of mutants ofNeurospora crassa (sor-1, sor-3, sor-4, sor-5, sor-6, sor-15, sor-T9, andpatch) were found to be resistant to the growth-inhibiting effect of sorbose.β(1–3)-Glucan synthase activity from each strain was found to be as sensitive to sorbose as wild-type enzyme activity. Four of these strains (sor-1, sor-4, sor-5, sor-T9) had altered sorbose transport; the remaining strains tested had normal sorbose transport. All of these strains (except forsor-3) were found to metabolize sorbose to glucose (and other compounds). This may explain their sorbose resistance.

γ-Ray-sensitive mutants of Neurospora crassa with characteristics analogous to ataxia telagiectasia cell lines

Well characterized γ-ray sensitive mutants of the fungus Neurospora crassa have been screened for characteristics analogous to those of cell lines derived from humans with the genetic disease, ataxia telagiectasia (AT). Two Neurospora mutants, uvs-6 and mus-9, show the AT cell line characterteristics of γ-ray and bleomycin sensitivity, and little or no repression of DNA synthesis following treatment with these agents. Norman human or Neurospora cells show an extensive biphasic DNA synthesis repression (to 50% of control) and when DNA synthesis is analyzed by alkaline gradient centrifugation, repression of DNA synthesis by low doses of γ-radiation occurs primarily in low molecular weight (MW) DNA pieces in both organisms. In AT cells and the uvs-6 mutant, no repression of low or higher MW DNA is seen at low doses, while the mus-9 mutant shows little repression of high MW DNA, but an intermediate level of low MW synthesis. Both mutants have been shown previously to have an increased level of spontaneous chromosome instability as do AT lines. The uvs-6 and mus-9 mutations are known to be due to two different genes in two different epistatic groups. These results demonstrate that AT-like cellular characteristics can arise from defects in at least two and probably any of several genes, and that lower eukaryotes such as Neurospora can provide an inexpensive and useful model for AT while avoiding the problems inherent in using transformed cell lines.

Circadian rhythms in Neurospora crassa: membrane composition of a mutant defective in temperature compensation

The cel mutant of Neurospora, partially blocked in fatty acid synthesis and lacking temperature compensation of its circadian rhythm below 22°C, had a phospholipid fatty acid composition in liquid shaker culture distinctly different from that of a cel + control strain. During growth, cel + exhibited a reproducible increase in its linoleic acid level from about 32 to a plateau at 63 mol%, and a corresponding decrease in its linolenic acid level from about 40 to a plateau at 10 mol%. The level of palmitic acid was constant at 19 mol%. In the cel strain, the linoleic acid level was constant at 54 mol% while the palmitic acid level increased from about 12 to about 23 mol%. Supplementation with palmitic or linoleic acids altered the patterns of fatty acid composition of cel, but did not affect the pattern of cel +. Altered fatty acid composition cosegregated with the cel marker. The mitochondrial phospholipids of cel in liquid culture also had abnormal fatty acid composition, as did the whole mycelial phospholipids on solid medium. These results are consistent with the involvement of membrane homeostasis in the temperature compensation of circadian rhythms.

Postmeiotic mitoses without chromosome replication in a mutagen-sensitive Neurospora mutant

In the recessive mutagen-sensitive mutant mus-8, no ascospores are formed. Ascospore delimiting membranes may be defective. Multiple postmeiotic mitoses occur, apparently without chromosome replication (at least at the first two mitoses). This results in many small nuclei, most of which contain only a few chromosomes or a single chromosome. These events resemble those in certain higher-plant mutants such as polymitotic in Zea mays.

Chromosome instability in mutagen sensitive mutants of Neurospora.

Four mutagen sensitive mutants of Neurospora (mus-7, mus-9, mus-11, and mei-2) are shown to increase mitotic chromosome instability in the duplication test developed by Newmeyer. Three other mutagen-sensitive mutants (upr-1, mus-8, and mus-10) do not increase chromosome instability. Previously three mutagen-sensitive mutants (uvs-3, uvs-6, and mei-3) were also shown to increase chromosome instability. The growth of all seven mutants that increase chromosome instability, is shown here to be more sensitive to hydroxyurea than that of wild type. Hydroxyurea, a compound which inhibits the enzyme ribonucleotide diphosphate reductase, is also shown to increase chromosome instability in the absence of any mutagen-sensitive mutation. These seven mutations are known to represent seven different genes in two epistasis groups. They have been shown previously to have four other properties in common: meiotic defects and sensitivity to gamma-rays, methyl methane sulfonate and the amino acid histidine. Their shared properties lead to the prediction here that all have reduced or altered deoxyribonucleotide pools.

Morphological mutant of Rhizoctonia solani and its cell wall component.

The perfect stage of Rhizoctonia solani Kuhn R-44 (Thanatephorus cucumeris) was confirmed by microscopic observation of basidiospores after three successive single spore isolations. A morphological mutant, ML-19, was induced by UV-light irradiation of a mycelial-fragment suspension from a single basidiospore culture of the fourth generation, and characterized. Different from in the cases of some kinds of morphological mutants of Neurospora, the morphology of this mutant was not responsible for conditional morphologicals, such as choline, inositol, linolenic acid and cAMP or hyphal extension factor. The characterization of the cell wall by fractionation, acid hydrolysis, Smith degradation and methylation analysis revealed that fraction III (glycan fraction) was composed of 1, 3-glucomannan containing small amounts of pentoses. The major difference in the fractions III from the original strain and the mutant was the change in the glucose/mannose ratio from 5/3 to 10/3.

Cloning of the ARO cluster gene of Neurospora crassa and its expression in Escherichia coli

We have constructed a phage, lambda Ncl, which comprises a 4.0 kb HindIII insert of Neurospora DNA into the immunity region of the vector lambda 598. lambda Ncl complements the aroD6 mutation of E. coli, permitting the formation of galaxy plaques on medium lacking aromatic supplements, and transforms an aro-9 qa-2 Neurospora mutant to prototrophy at a low frequency. Low levels of 5-dehydroquinate hydrolyase (E.C.4.2.1.10.), with properties unlike those of the catabolic isoenzyme that is coded by qa-2, are present in E. coli aroD6 cell lysates following infection with lambda Ncl. lambda Ncl does not hybridize with qa-2 DNA and it is concluded that it contains at least the aro-9 region of the pentafunctional aro cluster gene.

Neurospora mutants sensitive both to mutagens and to histidine

Previous work in this and other laboratories showed that histidine strongly inhibits growth of mutants at ten out of 20 known mutagen-sensitivity loci in Neurospora, and that nine of the histidine-sensitive mutants disturb meiosis when homozygous. These and other results suggested that histidine affects recombination or DNA repair. Current work with the histidine-sensitive mutant uvs-6 shows that it is also inhibited by several other metabolites but none of them is as effective as histidine. On minimal medium without histidine or other inhibitors, uvs-6 first grows normally, then slows drastically and begins stop-start growth. Conidia from stop-start uvs-6 mycelia produce rejuvenated cultures. The stop-start growth, UV-sensitivity, histidine-sensitivity, and recessive meiotic characters of uvs-6 segregated together in crosses, and reverted together. In tests on other mutagen-sensitive mutants, sensitivity to histidine was strongly correlated with stop-start growth and with sensitivity to other metabolites. Histidine induces premature stop-start growth in at least two mutants. Several possible explanations for the histidine-sensitivity have been excluded.

Excretion of pyruvate in nickel toxicity in wild type and Ni2+ resistant mutants ofNeurospora crassa

The parent wild strainNeurospora crassa Em 5297a and three Ni2+ resistantNeurospora crassa mutants have been shown to excrete pyruvate into the culture medium in Ni2+ and Co2+ toxicities. Ni2+ has a more pronounced effect in this regard. The excretion is progressive with growth inhibition and is abolished by Mg2+ in all strains and by Fe3+ partially in the Em strain but not inNeurospora crassa NiR1. Pyruvate, citrate and malate supplementation reverse growth inhibition caused by excess Ni2+, but with concomitant suppression of Ni2+ accumulation. It is suggested that one of the features of Ni2+ toxicity inNeurospora crassa is a derangement in carbohydrate metabolism at step(s) beyond pyruvate and that this is possibly due to decreased invivo activity of Mg2+ dependent processes

The [poky] mutant of Neurospora contains a 4-base-pair deletion at the 5' end of the mitochondrial small rRNA.

[ poky ] and other group I extranuclear mutants of Neurospora crassa are characterized by gross deficiencies of mitochondrial small ribosomal subunits and small (19S) rRNA. Blot-hybridization and other experiments suggest that the 19S rRNA (2.0 kilobases) is synthesized via precursors that contain 5'-end extensions. The ratio of precursors to mature rRNA is higher in [ poky ] and other group I mutants than in wild type, indicating that the defect involves impaired processing and/or instability of 19S rRNA. [ poky ] and other group I mutants contain a 4-base-pair deletion in the coding sequence for the mitochondrial small rRNA, just downstream from what would normally be the 5' end of the rRNA. This deletion apparently results in synthesis of aberrant 19S rRNAs that are missing 38-45 nucleotides from their 5' ends. We propose that the 4-base-pair deletion is the primary defect in [ poky ] and other group I extranuclear mutants.

Genetic control of cellular longevity in Neurospora crassa: A relationship between cyclic nucleotides, antioxidants, and antioxygenic enzymes

Short-lived conidial longevity mutants of Neurospora were studied. Mutations at a number of closely-linked and probably functionally-redundant genes lead to deficiency of five anti-oxygenic enzymes, including superoxide dismutase.

RNA splicing in neurospora mitochondria: Nuclear mutants defective in both splicing and 3′ end synthesis of the large rRNA

We have identified nuclear mutants of Neurospora that are defective in splicing the mitochondrial large rRNA and that accumulate unspliced pre-rRNA (35S RNA). In cyt-4 mutants, the unspliced pre-rRNA contains short 3′ end extensions (110 nucleotides) that are not present in pre-rRNAs from the other mutants. This and other characteristics suggest that the cyt-4 mutants may be primarily defective in 3′ end synthesis and the RNA splicing defect occurs secondarily as a result of impaired RNA folding. The cyt-4 mutants also accumulate a “short” intron RNA and small axon RNAs that may reflect aberrant RNA cleavages. The 5′ end of the short intron is about 285 nucleotides downstream from the 5′ splice site at or near the base of the “central hairpin”, a putative intermediate in folding of the pre-rRNA. Furthermore, the aberrant cleavage sites are immediately after a six nucleotide sequence (GAUAAU) homologous to the final splice junction (GAU/AAC).

DNA polymerase in temperature-sensitive mutants of Neurospora

DNA polymerase in temperature-sensitive mutants of Neurospora