Effects of cycloheximide and 5-fluorouracil on the synthesis of ribonucleic acid in yeast

Differential effect of the alkaloid lycorine on rho (+), mit (-), rho (-), and rho (o) strains of Saccharomyces cerevisiae

The alkaloid lycorine inhibits growth of rho (+), mit (-), and rho (-) strains, whereas rho (0) strains (devoid of mitochondrial DNA) of Saccharomyces cerevisiae are resistant to high concentrations of the drug. The inhibitory effect of lycorine on the growth of rho (+) strains can be counteracted by the addition of ascorbic acid to the plating medium. Lycorine induces cytoplasmic respiratory deficient mutants upon growth in glucose complete medium containing the alkaloid. The minimal inhibitory concentration of lycorine in glucose complete medium is ten times higher than in glycerol complete medium, thus demonstrating its preferential action on mitochondrial functions. Total protein synthesis and mitochondrial protein synthesis are only slightly inhibited by lycorine. It has, however, an inhibitory effect on DNA and RNA synthesis.

Interaction between yeast mitochondrial and nuclear genomes: null alleles of RTG genes affect resistance to the alkaloid lycorine in rho0 petites of Saccharomyces cerevisiae

Some nuclear genes in Saccharomyces cerevisiae (S. cerevisiae) respond to signals from the mitochondria in a process called by Butow (Cell Death Differ. 9 (2002) 1043-1045) retrograde regulation. Expression of these genes is activated in cells lacking mitochondrial function by involvement of RTG1, RTG2 and RTG3 genes whose protein products bind to "R-boxes" in the promoter region; RTG2p is a cytoplasmic protein. Since S. cerevisiae rho0 strains, lacking the entire mitochondrial genome, are resistant to lycorine, an alkaloid extracted from Amaryllis plants, it could be hypothesized that in rho0 cells the dysfunctional mitochondrial status stimulates overexpression of nuclear genes very likely involved in both nuclear and mitochondrial DNA replication. In this report we show that the resistance of rho0 cells to lycorine is affected by the deletion of RTG genes.

Dissociation of RNA synthesis from the calcium requirement for serum-increased ornithine decarboxylase activity in rat glioma cells

When C6-2B rat glioma cells were stimulated with calf serum in the presence of calcium, ornithine decarboxylase activity increased maximally in 6-8 h after an initial 2-3 h lag period wherein RNA synthesis occurred. The increase of ornithine decarboxylase activity in serum-stimulated C6-2B cells was prevented by the calcium chelator EGTA, but EGTA had no effect upon RNA synthesis as judged by [3H]uridine incorporation into RNA. In addition, the calcium requirement for increased ornithine decarboxylase activity was temporally distal to the lag period. EGTA appeared to inhibit the synthesis of ornithine decarboxylase, because the half-life values of ornithine decarboxylase activity were similar (37-47 min) in the presence of EGTA or protein synthesis inhibitors such as cycloheximide or emetine. Also, calcium readdition rapidly reversed EGTA inhibition of ornithine decarboxylase activity by a mechanism which could be blocked by cycloheximide.

Blue light-dependent regulation of cytoplasmic ribosomal RNA synthesis in Chlorella

Effect of blue and red light on ribosomal RNA synthesis in autotrophic synchronous cultures of Chlorella pyrenoidosa (strain 211-8b) is studied by pulse labeling experiments with tritiated guanosine. Nucleic acids were separated by electrophoresis on polyacrylamide gels. Compared with darkness and red light (679 nm), blue light (457 nm) of equal quantum flux (0.5-5x10(-10) Einstein cm-2 s-1) stimulates incorporation into ribosomal RNA. This blue light effect is observed in the cytoplasmic ribosomal RNA after 5 min of illumination, whereas the stimulation of chloroplast ribosomal RNA synthesis by blue light appears later. Maturation of chloroplast ribosomal RNA is slower than that of cytoplasmic ribosomal RNA. The blue light effect on the cytoplasmic ribosomal RNA formation does not require chloroplast RNA or protein synthesis as shown by inhibitor studies with rifampicin or lincomycin. The blocking of cytoplasmic protein synthesis by cycloheximide inhibits the blue light effect on ribosomal RNA formation. It is concluded that the cytoplasmic ribosomal RNA transcription is controlled by a blue light sensitive system.

Evidence for cycloheximide acting as a glutamine analogue in plant tissue

In growing maize root tissue [14C]asparagine formation in inhibited and [14C]glutamine accumulation stimulated by treatment with cycloheximide or glutamine analogs such as azaserine. In contrast, puromycin enhances the accumulation of [14C]asparagine but not [14C]glutamine. Cycloheximide and puromycin alone inhibit protein synthesis. This is interpreted to mean that the alteration in amide metabolism following cycloheximide treatment is a direct result of the antibiotic acting as a glutamine analog. While cycloheximide is often the cytoplasmic protein synthesis inhibitor of choice due to its potency and rapid action, its assumed specificity of action of eukaryotes is doubtful.

Photoregulation of transfer and 5S ribosomal RNA synthesis in Chlorella

The effect of blue and red light on the synthesis of transfer and 5S ribosomal RNA in autotrophic cultures of Chlorella pyrenoidosa was studied by pulse labeling experiments with tritiated guanosine. Compared with darkness or red light (679 nm), blue light (457 nm) of low intensities (quantum flux: 0.5-5×10(-10) mol photons cm(-2) s(-1)) stimulated incorporation of guanosine into transfer and 5S ribosomal RNA within the first 5 min of illumination. This blue light effect was abolished by cycloheximide, an inhibitor of protein synthesis on 80S ribosomes, but not by rifampicin, an inhibitor of chloroplastic transcription, nor by lincomycin, an inhibitor of chloroplastic translation. The rifampicin-insensitive synthesis of transfer and 5S ribosomal RNA was nuclear transcription as shown by RNA-DNA hybridization. The blue light effect on nuclear RNA synthesis was not inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea, an inhibitor of photosynthesis electron transport. Further evidence for a photosynthesis-independent photocontrol of RNA synthesis was provided by experiments with the colorless mutant 125a of Chlorella vulgaris. Blue light stimulated incorporation of guanosine into cytoplasmic 25S and 18S ribosomal RNA as well as into transfer and 5S ribosomal RNA, whereas incorporation in red light was the same as that of the dark control.

Methylated nucleosides in polyadenylate-containing yeast messenger ribonucleic acid

Yeast messenger RNA was found to be methylated. A calculation of the specific methylation showed that the average yeast messenger RNA molecule contains only two methylated nucleosides which occur in one alkali stable oligonucleotide. Similar to other eukaryotic messengers, the 5' terminus of yeast messenger RNA is blocked by 7-methylguanosine, linked through a di- or triphosphate bridge to a ribosemethylated nucleoside. Contrary to the messengers of high eucaryotic organisms, no additional base methylated constituents were found.

Effects of cycloheximide and 5-fluorouracil on formation of low-molecular-weight ribonucleic acid in yeast

The effects of cycloheximide and 5-fluorouracil on the formation of low-molecular-weight ribonucleic acid (RNA) in yeast were investigated. Both compounds were found to affect the synthesis of low-molecular-weight RNA of ribosomal origin more than transfer RNA but less than the high-molecular-weight ribosomal RNA. 5-Fluorouracil-containing transfer RNA was separated from normal transfer RNA by chromatography on diethylaminoethyl cellulose at 80 C in the presence of 7 m urea.