CHARACTERISTICS OF 5-FLUOROURACIL-INDUCED SYNTHESIS OF ALKALINE PHOSPHATASE

A novel form of suppression due to an altered RNA polymerase

A group of mutants isolated from E coli K12(tif-1) display a very pleiotropic phenotype. The main characteristic of these mutants, temporarily designated 'S' strains, is their ability to suppress a large number of mutations. High efficiency of suppression is correlated with increased thermolability of cellular proteins, indicating an impairment in the fidelity of protein synthesis. Efficient suppression is also accompanied by the appearance of new characteristics like simultaneous resistance to several antibiotic drugs (Sm, Spc, and Mer), and plasmid-like DNA circles. Genetic studies show that the suppressor character is located in the rpoBC region. In a large number of spontaneous Rifr mutants, isolated from these strains, suppression or resistance to drugs is lost. The findings suggest that the phenotype of 'S' strains is due to an altered RNA polymerase causing erroneous transcription.

Character of the stimulatory response of uridine kinase in rat livers to cycloheximide treatment

Administration of cycloheximde to adult rats resulted in the enhancement of uridine kinase activity in the liver. The increase of enzyme activity was not affected by adrenal secretion or uptake of food. Actinomycin D, hydroxyurea and puromycin injected simultaneously with cycloheximide depressed the increase of enzyme activity. On the contrary, administration of 5-azacytidine following cycloheximide resulted in further enhancement of uridine kinase. While the half-time of template RNA for uridine kinase in control rat livers was 24 h, for cycloheximide-stimulated enzyme it was about 11 h. At higher dose levels cycloheximide leads to an increased incorporation of both uridine and orotic acid into liver RNA; however, this effect was not observed in the starved animals. The mechanism of action of cycloheximide is briefly mentioned.

In vivo suppression of coding associated with bacteriophage-induced S-adenosylmethionine hydrolase

The methylation of ribosomal and transfer ribonucleic acid (RNA) synthesized after the induction of a hydrolase for S-adenosylmethionine by phage T3 infection is reducible to 50% of the methylation of RNA in uninfected cells. Hypomethylated ribosomal RNA is found in 70S particles that dissociate in 100 mum Mg(++) to yield only 30S and 50S subunits. By this criterion, the omitted methyl groups apparently are not required for ribosomal maturation or stability. The rate of production of alkaline phosphatase in a phosphatase amber mutant was examined after phage infection in the presence and in the absence of streptomycin to determine the effect on the translation process consequent to S-adenosyl-l-methionine (SAM) hydrolase induction. Significant increases in the rates of phosphatase production were found when ultraviolet-inactivated T3 or streptomycin was added. The effects were cumulative when the cells were treated with both bacteriophage and the drug. Ultraviolet-inactivated T7, a phage closely related to T3 but which does not produce the SAM hydrolase, did not enhance the rate of alkaline phosphatase production. We suggest that the production of SAM hydrolase affects the stability of the translation process by the observed hypomethylation or by mechanisms concerning polyamine metabolism.

Decay of normal and 5-fluorouracil-substituted messenger ribonucleic acid of alkaline phosphatase in Escherichia coli

The decay of alkaline phosphatase messenger ribonucleic acid (mRNA) in Escherichia coli was studied in cells sensitized to actinomycin D by ethylenediaminetetra-acetate treatment. It was found that in the wild-type strain (K-10) as well as in a nonsense mutant (S26C200), which is phenotypically reversible by treatment with 5-fluorouracil, mRNA decays with a half-life of 2.0 to 2.5 min. Similarly, in a 3-min pulse of labeled 5-fluorouracil, 70% of the incorporated analogue is contained in the labile RNA fraction decomposing with a half-life of 1.8 min.

Morphogenesis in Trichoderma: suppression of photoinduction by 5-fluorouracil

Sporulation in the fungus Trichoderma viride is inducible with a short light pulse. 5-Fluorouracil applied prior to photoinduction and removed thereafter suppressed sporulation without greatly aflecting growth. This compound also halved the rate of incorporation of uracil-C(14) into RNA but did not change the ratio of uridylic to cytidylic acid. The effect of 5-fluorouracil was counteracted by uracil but not by thymidine. This supports the hypothesis that 5-fluorouracil affects RNA rather than DNA.