Ribonucleic acid synthesis in yeast. The effect of cycloheximide on the synthesis of ribonucleic acid in Saccharomyces carlsbergensis

Molecular Basis for a Cell Fate Switch in Response to Impaired Ribosome Biogenesis in the Arabidopsis Root Epidermis

The Arabidopsis (Arabidopsis thaliana) root epidermis consists of a position-dependent pattern of root hair cells and non-hair cells. Underlying this cell type patterning is a network of transcription factors including a central MYB-basic helix-loop-helix-WD40 complex containing WEREWOLF (WER), GLABRA3 (GL3)/ENHANCER OF GLABRA3, and TRANSPARENT TESTA GLABRA1. In this study, we used a genetic enhancer screen to identify apum23-4, a mutant allele of the ribosome biogenesis factor (RBF) gene ARABIDOPSIS PUMILIO23 (APUM23), which caused prospective root hair cells to instead adopt the non-hair cell fate. We discovered that this cell fate switch relied on MYB23, a MYB protein encoded by a WER target gene and acting redundantly with WER. In the apum23-4 mutant, MYB23 exhibited ectopic expression that was WER independent and instead required ANAC082, a recently identified ribosomal stress response mediator. We examined additional RBF mutants that produced ectopic non-hair cells and determined that this cell fate switch is generally linked to defects in ribosome biogenesis. Furthermore, the flagellin peptide flg22 triggers the ANAC082-MYB23-GL2 pathway. Taken together, our study provides a molecular explanation for root epidermal cell fate switch in response to ribosomal defects and, more generally, it demonstrates a novel regulatory connection between stress conditions and cell fate control in plants.

Reduction in ribosomal protein synthesis is sufficient to explain major effects on ribosome production after short-term TOR inactivation in Saccharomyces cerevisiae

Ribosome synthesis depends on nutrient availability, sensed by the target of rapamycin (TOR) signaling pathway in eukaryotes. TOR inactivation affects ribosome biogenesis at the level of rRNA gene transcription, expression of ribosomal proteins (r-proteins) and biogenesis factors, preribosome processing, and transport. Here, we demonstrate that upon TOR inactivation, levels of newly synthesized ribosomal subunits drop drastically before the integrity of the RNA polymerase I apparatus is severely impaired but in good correlation with a sharp decrease in r-protein production. Inhibition of translation by cycloheximide mimics the rRNA maturation defect observed immediately after TOR inactivation. Both cycloheximide addition and the depletion of individual r-proteins also reproduce TOR-dependent nucleolar entrapment of specific ribosomal precursor complexes. We suggest that shortage of newly synthesized r-proteins after short-term TOR inactivation is sufficient to explain most of the observed effects on ribosome production.

Selective inactivation of two components of the multiprotein transcription factor TFIIIB in cycloheximide growth-arrested yeast cells

Following protein synthesis inhibition in cycloheximide growth-arrested yeast cells, the rates of tRNA and 5 S RNA synthesis decrease with apparent half-times of about 20 and 10 min, respectively. This effect is mimicked by extracts of treated cells, and the impairment of tRNA gene transcription activity that is observed in vitro parallels the in vivo inactivation of RNA polymerase III transcription. As revealed by experiments in which partially purified class III transcription factors were singly added to extracts of treated cells, only the activity of the multiprotein transcription factor TFIIIB is severely impaired after 3 h of cycloheximide treatment. Similar assays carried out in an in vitro transcription system in which TFIIIB activity was reconstituted by a combination of the TATA box-binding protein (TBP), the 70-kDa component TFIIIB70, plus a partially purified fraction known as B" have shown that the latter two components are both necessary and sufficient to restore control levels of transcription. Their activity, but not TBP activity, is considerably reduced in extracts of treated cells. TFIIIB70 and a component of fraction B" thus appear to be the selective targets of the down-regulation of polymerase III transcription that is brought about by cycloheximide. A substantial depletion of the TFIIIB70 polypeptide was detected by Western immunoblot analysis of extracts derived from cycloheximide growth-arrested cells, indicating that the inactivation of this TFIIIB component results primarily from its enhanced destabilization under conditions of protein synthesis inhibition.

Isolation and characterization of mutants defective in production of laccase in Neurospora crassa

A protein synthesis inhibitor, cycloheximide, induces excretion of laccase in Neurospora crassa. The lah-1 mutation results in excretion of a large amount of laccase even in the absence of cycloheximide. Ten mutations were induced that suppress derepressed excretion of laccase in the lah-1 mutant. Of these, seven second-site mutations were found to confer a laccase-noninducible phenotype, and were classified into two different complementation groups. Four mutations define a locus designated lni-1, found to be closely linked to ylo-1 on linkage group VI. The other three mutations were mapped to second locus, designated lni-2, that lies between nic-3 and thi-3 on linkage group VII. The lni-2 locus was shown to encode laccase by RFLP mapping of the DNA fragment encoding laccase and by transformation of the lni-2 mutant with plasmid pBL1 carrying the laccase gene (the locus encoding laccas is hereafter described as lacc). All lacc mutants examined (whether mutagen-induced or inactivated by repeat-induced point mutation) appeared to exhibit no phenotypic deficiency during both asexual and sexual cycles, suggesting that the laccase gene is dispensable in N. crassa. Northern analysis of total cellular RNA from the four lni-1 mutants demonstrated that the lni-1 mutations abolish increased transcription of the laccase gene under inducing conditions. Consequently, the lni-1 locus is inferred to encode a trans-acting positive regulator required for transcriptional activation of the laccase gene in response to cycloheximide. Possible functions of the lah-1 gene are also described.

Studies on the regulation of enolases and compartmentation of cytosolic enzymes in Saccharomyces cerevisiae

Three enolase isoenzymes can be distinguished after electrophoresis of yeast crude extracts. After adding glucose to derepressed cells, there was a coordinated increase in the activity of enolase I and decrease in enolase II activity. Enolase I was found to be repressed and enolase II simultaneously induced by glucose. The third enolase activity remained unchanged and was identified as that of a hybrid enzyme. Enolase catalyses the first common step of glycolysis and gluconeogenesis. Gluconeogenic enolase I shows substrate inhibition for 2-phosphoglycerate (glycolytic substrate) and glycolytic enolase II is substrate-inhibited by phosphoenolpyruvate (gluconeogenic substrate). The gluconeogenic reaction was inhibited up to 45% by physiological concentrations of fructose 1,6-bisphosphate. To test for cytological compartmentation, a method was developed for isolating microsomes. Effective enrichment of rough and smooth endoplasmic reticulum was demonstrated by electron microscopy. No evidence was obtained for any compartmentation of either enolases or other glycolytic enzymes.

Evidence for separate elongation enzymes for very-long-chain-fatty-acid synthesis in potato (Solanum tuberosum)

Aging potato (Solanum tuberosum) tuber discs in a Ca2+-containing medium resulted in increased rates of fatty acid labelling from [1-14C]acetate with time. Maximal labelling rates were seen after 6-8 h aging in a number of varieties. Saturated very-long-chain fatty acids (C20 and particularly C22 and C24) were very poorly labelled in freshly cut tissue. They were synthesized in increasing amounts and in a homologous sequence with progressive aging times. Use of increasing induction times and cycloheximide or puromycin as protein-synthesis inhibitors indicated that the sequence of fatty acid elongation was dependent on protein synthesis de novo and was controlled by three separate specific elongase enzymes.

Characterization of an essential Saccharomyces cerevisiae gene related to RNA processing: cloning of RNA1 and generation of a new allele with a novel phenotype

The RNA1 gene product is believed to be involved in RNA metabolism due to the phenotype of a single conditionally lethal, temperature-sensitive allele, rna1-1. We cloned the RNA1 gene and determined that it produces a 1,400-nucleotide polyadenylated transcript. On a multicopy plasmid, the mutant rna1-1 allele partially complements the rna1-1 temperature-sensitive growth defect. This suggests that the temperature-sensitive nature of the rna1-1 allele results from the synthesis of a product with lowered activity or stability at elevated temperatures or from a decrease in synthesis of the rna1-1 product at the restrictive temperature. A chromosomal disruption of RNA1 behaves as a recessive lethal mutation. Haploids bearing the disruption were isolated by sporulating a diploid heterozygous for the disrupted allele and the rna1-1 allele and possessing an episomal copy of the RNA1 gene. Analysis of the rescued haploids bearing the chromosomal disruption indicated that the recessive lethal phenotype of the RNA1 disruption is not merely due to a block in spore germination. Unexpectedly, diploids heterozygous for the disruption and the rna1-1 alleles become aneuploid for chromosome XIII at a frequency of 2 to 5%. It appears that the disrupted RNA1 allele on a multicopy plasmid also promotes aneuploidy for chromosome XIII. Promotion of aneuploidy seems to be a phenotype of this particular allele of RNA1.

Characterization of an essential Saccharomyces cerevisiae gene related to RNA processing: cloning of RNA1 and generation of a new allele with a novel phenotype

The RNA1 gene product is believed to be involved in RNA metabolism due to the phenotype of a single conditionally lethal, temperature-sensitive allele, rna1-1. We cloned the RNA1 gene and determined that it produces a 1,400-nucleotide polyadenylated transcript. On a multicopy plasmid, the mutant rna1-1 allele partially complements the rna1-1 temperature-sensitive growth defect. This suggests that the temperature-sensitive nature of the rna1-1 allele results from the synthesis of a product with lowered activity or stability at elevated temperatures or from a decrease in synthesis of the rna1-1 product at the restrictive temperature. A chromosomal disruption of RNA1 behaves as a recessive lethal mutation. Haploids bearing the disruption were isolated by sporulating a diploid heterozygous for the disrupted allele and the rna1-1 allele and possessing an episomal copy of the RNA1 gene. Analysis of the rescued haploids bearing the chromosomal disruption indicated that the recessive lethal phenotype of the RNA1 disruption is not merely due to a block in spore germination. Unexpectedly, diploids heterozygous for the disruption and the rna1-1 alleles become aneuploid for chromosome XIII at a frequency of 2 to 5%. It appears that the disrupted RNA1 allele on a multicopy plasmid also promotes aneuploidy for chromosome XIII. Promotion of aneuploidy seems to be a phenotype of this particular allele of RNA1.

The regulation of RNA synthesis in yeast. V. tRNA charging studies

The stringent control of RNA synthesis in the yeast Saccharomyces cerevisiae may be evoked either by starving for a required amino acid or by inhibiting protein synthesis. The response is non-coordinate in that the synthesis of ribosomal and messenger RNA is depressed whereas that of transfer RNA continues. If protein synthesis is blocked in starved cells then tRNA synthesis is stimulated. In this paper, the relationship between the level of tRNA charging and the transcriptional and translational state of the yeast cell has been examined. When cells are starved for an amino acid the corresponding tRNA species only becomes uncharged. This effect can be counteracted by the addition of protein synthesis inhibitors to the starved cells. In contrast, the same inhibitors provoked the discharge of tRNA in growing (non-starved) yeast. Similar results were obtained when protein synthesis was blocked using a temperature-sensitive mutant. These contrasting effects of translation inhibition on tRNA charging in starved and non-starved cells correlate with the changes that inhibition evoked in the transcriptional state of those cells. The data indicate that tRNA synthesis is under autoregulatory control and that tRNA charging may also play an important role in the regulation of rRNA synthesis.

Ribosomal RNA transcription in a mutant of Saccharomyces cerevisiae defective in ribosomal protein synthesis

In Saccharomyces cerevisiae, the transcription of ribosomal precursor RNA is severely inhibited in the absence of protein synthesis. However, such transcription is not dependent on the synthesis of ribosomal proteins, nor on the synthesis of mRNA for ribosomal proteins, nor on the processing of ribosomal precursor RNA.

The regulation of RNA synthesis in yeast. I: Starvation experiments

The synthesis of tRNA in yeast is shown to be under separate control to that of rRNA during amino acid and nitrogen starvation. Inhibitors of the elongation and termination steps of protein synthesis were found to stimulate the synthesis of tRNA in starved yeast cells. This effect appeared to be due to the "trickle-charging" of tRNA. Two inhibitors of early steps in the initiation of protein synthesis were found to be unable to stimulate RNA synthesis in starved cells. It is proposed that yeast tRNA synthesis is under autoregulatory control and that the level of tRNA charging and the mRNA-ribosome complex are important components of this control system.

Effect of cycloheximide on RNA synthesis in Chironomus polytene chromosomes

Modifications in the synthesis of salivary gland RNA were induced by treatments with 10 microgram/ml cycloheximide (CHM) on 4th instar larvae of Chironomus pallidivitattus. After 3, 6 and 24 h CHM treatment, RNA was labeled "in vitro", by incubating the salivary glands in a medium containing H3-uridine. The electrophoretical analyses corresponding to the 3 and 6 h treatment showed a stimulation of the non-ribosomal components of the newly synthesized RNA, while preribosomal RNA synthesis appeared depressed. This fact was also confirmed at cytological level, since autoradiograms made after 3 h of CHM treatment showed a reduced H3-uridine label over the nucleolus and an increase of diffuse labeling over the chromosomes. Longer treatments (24 h) causes a considerable inhibition of the synthesis of all RNA species. The role played by protein synthesis inhibition in the aforementioned effects is discussed.--Some of the morphological implications of CHM treatment, such as modifications of the nucleolar structure (nucleolar segregation) are also reported. The use of a squash technique based on glutaraldehyde fixation of the salivary glands, considerably facilitates such studies.

Effect of puromycin on synthesis, processing, and nucleocytoplasmic translocation of rRNA in Tetrahymena pyriformis

1. Treatment of Tetrahymena pyriformis with various concentrations of puromycin results in a more pronounced inhibition of [3H]uridine accumulation in stable RNA than of protein synthesis. 2. At a concentration of 500 micrograms/ml, which is almost completely inhibitory to [3H]uridine incorporation in vivo, puromycin has no influence on the incorporation of [3H]UTP into RNA in isolated macronuclei. Pretreatment of the cells with the antibiotic, however, reduces the activity of RNA polymerases in isolated nuclei to less than 30%. 3. In puromycin-treated cells a small amount of pre-rRNA is synthesized but not processed into cytoplasmic rRNAs. 4. Puromycin reduces the nucleocytoplasmic translocation of pre-existing RNA to about 25% of the control rate within 5 min, resulting in an accumulation of relatively stable rRNA precursor molecules in the macronucleus.

Stoffwechselprodukte von mikroorganismen. 154. Mitteilung. Nikkomycin, ein neuer hemmstoff der chitinsynthese bei pilzen

From the fermentation broth of Streptomyces tendae Tü 901 a substance was isolated which inhibits the growth of several fungi. The new antibiotic affects the chitchin biosynthesis. Its structure was identified by mass spectrometry of the products obtained after chemical degradation. Nikkomycin is a nucleoside-peptide antibiotic consisting of uracil, an amino hexuronic acid and a new amino acid containing a pyridin ring.

Studies on the control of ribosomal RNA synthesis in HeLa cells

In many eucaryotic systems protein synthesis is coupled to ribosomal RNA synthesis such that shut-down of the former causes inhibition of the latter. We have investigated this stringency phenomenon in HeLa cells. The protein synthesis inhibitors cycloheximide and puromycin cause inactivation of both processes but valine starvation totally inhibits only the processing of 45-S RNA. DNA-dependent RNA polymerases from A, B and C (or I, II and III respectively) were extracted, separated partially by DEAE-cellulose chromatography and their activity levels determined. These do not decrease significantly during inhibition of protein synthesis. To find out whether or not form A is bound to its template under these conditions, proteins were removed from chromatin with the detergent sarkosyl. This does not affect bound RNA polymerase. Inhibition of protein synthesis caused up to 50% reduction in endogenous alpha-amanitin-insensitive chromatin-RNA-synthesising activity. This reduced level of activity was not affected by sarkosyl treatment. Levels in normal cells were stimulated. This result indicates that the form A RNA polymerase is not bound to its template when protein synthesis is inhibited.

Cycloheximide is not a specific inhibitor of protein synthesis in vivo

Cycloheximide is frequently presumed to inhibit specifically the cytoplasmic protein synthesis of eukaryotes. Although previous investigators have shown that it had other effects on the cells of a variety of organisms, these results were frequently presumed to be secondary effects of the inhibition of protein synthesis. This paper shows that a wide range of deleterious effects are produced by cycloheximide on a single organism, Chlamydomonas reinhardi Dangeard. If, protein synthesis is inhibited by nonpermissive conditions in temperature-sensitive mutants or with other treatments these "secondary" effects are not produced. Instead, cycloheximide appears to have two or three independent inhibitory effects on the cell. Moreover, in contrast to a number of previous investigations, these results show that protein synthesis is not required for RNA synthesis. Instead the rate of RNA synthesis is actually increased by interference with protein synthesis.

Differential effects of analogs of cycloheximide on protein and RNA synthesis in Achlya

Analogs of the glutarimide antibiotic cycloheximide were tested for their effect on growth and incorporation of proline and uridine into acid-insoluble material in Achlya bisexualis. Each of the compounds tested had reduced antibiotic activity as compared to cycloheximide. The effects of the antibiotics on protein and RNA synthesis were varied. While cycloheximide inhibited both protein and RNA synthesis immediately, two of the analogs inhibited proline incorporation without effect on uridine incorporation, while three, each representing a modification of the hydroxyl of cycloheximide, stimulated uridine incorporation and either had no effect on or inhibited protein synthesis. These results indicate that the control of RNA synthesis by protein synthesis in Achlya can be released by glutarimide antibiotics.

Protein synthesis during the differentiation of sporangia in the water mold Achlya

During the synchronous differentiation of sporangia in the absence of added nutrients, the water mold Achlya bisexualis (Coker and Couch) actively synthesized protein. Inhibition of protein synthesis at any time during the sporulation process completely inhibited further differentiation. Large changes in the rate of radioactive amino acid uptake resulted in changes in the specific activity of the cellular amino acid pool. The rate of protein synthesis was calculated from the amino acid pool specific activity and the incorporation of isotope into protein. During the 1st h after induction of the sporulation process, the rate of protein synthesis increased to two times the initial value. The amino acid precursors for this synthesis were supplied by the degradation of preexisting protein. Proteolytic enzyme activity assayed in vitro increased in proportion to the in vivo rates of protein synthesis and degradation. Differentiation was accompanied by a slight decline in dry weight of the mycelium as well as by a decrease in the protein content, whereas the relative size of the amino acid pools remained constant.

Distribution of ribosomal ribonucleic acid cistrons among yeast chromosomes

High-molecular-weight deoxyribonucleic acid (DNA) of Saccharomyces carls bergensis has been fractionated by sucrose density gradient centrifugation. The main DNA fraction has an average molecular weight of about 500 x 10(6). A major fraction of the DNA molecules containing sequences homologous to ribosomal ribonucleic acid (RNA) sediments as material of this molecular weight. The remainder sediments as material of a molecular weight of about 250 x 10(6). The latter fraction contains relatively more ribosomal RNA cistrons than the former. Studies on the buoyant density of high-molecular-weight DNA homologous to ribosomal RNA have led to the conclusion that the ribosomal RNA cistrons occur in groups attached to a relatively large amount of nonribosomal RNA and suggest that ribosomal RNA cistrons are distributed over a number of yeast chromosomes.

The rapid turnover of RNA polymerase of rat liver nucleolus, and of its messenger RNA

Turnover rates of the components of systems for RNA synthesis of rat-liver nucleus, nucleolus, and nucleoplasm were investigated. Cycloheximide administered in vivo selectively diminished nucleolar RNA synthesis in vitro. In contrast to the relatively stable nucleoplasmic RNA polymerase, nucleolar RNA polymerase (polymerase I) from rat liver decays rapidly upon cycloheximide administration, following pseudo-first order kinetics with a half-life of about 1.3 hr. Cycloheximide elicits this effect not through direct interaction with nucleolar RNA polymerase itself, nor by alteration of template function, but rather by inhibition of de novo synthesis of one or more of the protein components of nucleolar RNA polymerase. Similarly, when actinomycin-D was administered in vivo to inhibit RNA synthesis, the rate of decay of nucleolar RNA polymerase, assayed in the presence of exogenous poly d(A-T) template, was similar to that observed after cycloheximide administration. Thus, the messenger RNA(s) that codes for one or more of the catalytically essential polypeptide components of this enzyme turn over very rapidly with a half-life considerably shorter than 1.3 hr. The rapidity of turnover of both the enzyme protein and its messenger RNA(s) renders nucleolar RNA polymerase highly responsive to altered transcriptional, translational, or post-translational modulation. The marked differences in turnover rates of nucleolar and nucleoplasmic RNA polymerases indicate that at least certain of the protomeric components of nucleolar RNA polymerase I are distinct from those of nucleoplasmic RNA polymerases II and III.

Dependence of ribonucleic acid synthesis on continuous protein synthesis in yeast

Using an auxotrophic strain of Saccharomyces cerevisiae, we examined the kinetics of ribonucleic acid (RNA) synthesis following inhibition of protein synthesis caused by amino acid starvation or cycloheximide. Removal of a required amino acid immediately stopped net protein synthesis. After a brief lag, RNA synthesis also ceased. Cycloheximide, a ribosome-inhibiting drug, also immediately halted net protein synthesis. Again RNA synthesis stopped after a brief lag. Although cycloheximide and amino acid starvation affect different steps in protein biosynthesis, both inhibited RNA synthesis in identical fashion. This indicates that amino acids do not play a unique role in the control of RNA production in rapidly growing yeast; rather, it suggests that RNA synthesis is responsive to the overall rate of protein synthesis itself.

Cell wall synthesis in yeast protoplasts

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Osmotic regulation of invertase formation and secretion by protoplasts of Saccharomyces

Osmotic regulation of invertase formation and secretion by protoplasts of Saccharomyces was examined using sorbitol, KCl, NaCl, or magnesium sulfate as the osmotic support. The synthesis and secretion of the enzyme is remarkably sensitive to the osmolarity of the supporting medium irrespective of the particular support employed. Invertase formation was inhibited at high osmolarity and was maximal at 0.65 to 0.75 osmolal, even though some leakage of the intracellular enzyme alpha-glucosidase and of ultraviolet (UV)-absorbing materials occurred under these conditions. The reduction of invertase formation and secretion due to high osmolarity was eliminated promptly when protoplasts were transferred into a medium of lower osmolarity. The rate of fructose uptake and of threonine incorporation into protein was decreased by high osmolarity; also reduction of invertase formation could be partially reversed by increasing the level of sugar supplied as energy source. Thus changes in the permeability of the plasma membrane (and presumably also in its structure) are important factors in the response of protoplasts to high osmolarity, though certainly not the complete explanation. Protoplasts suspended in 0.8 m sorbitol, with 10mm fructose as the energy source, increased their invertase level 5- to 10-fold during a 2-hr incubation without substantial release of alpha-glucosidase or UV-absorbing materials. Both the large and small forms of invertase were present in the protoplasts, but only the large form was released into the medium when enzyme was being actively synthesized. Formation and secretion of newly formed invertase and the release of enzyme initially present were inhibited by cycloheximide.

Isolation and properties of a new species of ribonucleic acid synthesized in sporulating cells of Saccharomyces cerevisiae

A new species of ribonucleic acid (RNA) was detected in sporulating culture of Saccharomyces cerevisiae. This RNA was isolated by sucrose density gradient centrifugation and polyacrylamide gel electrophoresis and partially characterized. It has a sedimentation coefficient of approximately 20S and a nucleotide composition distinct from other known RNA species in yeast, and it hybridizes with nuclear but not with mitochondrial deoxyribonucleic acid.