In vitro effect of cycloheximide on the nucleolar and extranucleolar nuclear RNA polymerases of rat liver

Amino acid analogs inhibit murine xenotropic retrovirus expression and cell cycle progression

Certain functional analogs of amino acids were examined for their capacity to inhibit chemically induced expression of endogenous xenotropic retrovirus from Kirsten sarcoma virus transformed BALB/c (K-BALB) mouse cells. Partially synchronized cells cultured with aminoethylcysteine (AEC), parafluorophenylalanine (PFA), or valinol, and subsequently induced with either 5-iododeoxyuridine (IUdR), cycloheximide, or histidinol, showed inhibition of virus activation. Inhibition was concentration- and time-dependent (1 to 4 h) and not a consequence of cytotoxicity. Inhibition was competed out by the analogous amino acid and was specific to the induction process. After a 4 h analog treatment, heteronuclear RNA synthesis was reduced 24, 38, and 35% by PFA, AEC, and valinol, respectively, whereas cycloheximide or actinomycin D reduced synthesis by 60 and 90%, respectively; therefore, the analogs did not seem to inhibit induction through a general transcriptional block. Culture of cells in the presence of the analogs resulted in an abrupt reduction (70 to 90%) in DNA synthesis. Using synchronized cells, it was found that 0.1 mM AEC added in G1 phase and followed by IUdR induction almost totally inhibited virus expression. No inhibition was observed when AEC was added during S phase concomitantly with the inducer. AEC added to synchronous cells in G1 phase inhibited the progression of cells into S phase and the onset of DNA synthesis. The results show that K-BALB cells have an AEC-sensitive restriction point in G1 phase that might relate to the effects amino acid analogs have on cell replication and S phase dependent gene expression, as well as subsequent differentiation.

Effect of cycloheximide on the in vivo and in vitro synthesis of ribosomal RNA in rat liver

The action of low (5 mg/kg body wt;) and high (20 mg/kg body wt.) doses of cycloheximide, both causing a rapid and almost complete inhibition of protein synthesis in rat liver is investigated. Short-term (15 min) [14C]orotate incorporation into nucleolar rRNA in vivo is inhibited only by the high dose acting for periods longer than 1 h. The effect may be correlated with a strongly reduced labelling of the cellular pool of free uridine nucleotides. These results indicate that in vivo transcription of rRNA genes may not be under stringent control. The activity of template-bound RNA polymerase A in nuclei isolated from animals treated with both doses of cycloheximide is reduced within 1 h to about 50% of controls reaching nearly plateau levels at longer times of action of the drug. The differential effect of cycloheximide inhibition of protein synthesis on in vivo and in vitro rRNA synthesis suggests the existence of elongation control protein(s) characterized by a rapid turnover and a loose association with the nucleus.

Regulation of mammalian protein synthesis in vivo. Stimulated liver ribonucleic acid synthesis in vivo after cycloheximide treatment

1. As shown by a double-radioisotope technique in vivo, at a non-lethal dose of cycloheximide, a stimulation of nuclear RNA synthesis occurred by 12 h after the treatment; the stimulation lasted over 48 h. Analysis of radioactive nuclear RNA by gel electrophoresis demonstrated that most of the cycloheximide-stimulated synthesis could be accounted for by known rRNA precursors (45 S, 41 S, 32 S and 28 S). 2. During the inhibitory phase of protein synthesis, 2 h after cycloheximide treatment, synthesis of the poly(A)-containing mRNA isolated from the cytoplasmic ribonucleoprotein complexes with an oligo(dT)-cellulose column was stimulated, whereas the synthesis of rRNA was slightly inhibited. However, during the stimulatory phase of protein synthesis, 24 h after cycloheximide treatment, the syntheses of both poly(A)-containing mRNA and rRNA were enhanced. 3. Kinetic studies revealed that the newly synthesized RNA species were transported from the nuclei, integrated into the ribonucleoprotein complexes, and associated with both free and membrane-bound polyribosomes. 4. These data corroborate our proposal that the stimulated protein synthesis after cycloheximide administration involves gene transcription.

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.

Ribonucleic acid polymerase in Allomyces arbuscula

Three distinct species of ribonucleic acid (RNA) polymerase were resolved from Allomyces arbuscula by diethylaminoethyl-cellulose chromatography and characterized as to ionic strength and divalent cation preference. alpha-Amanitin specifically inhibited enzyme II; neither rifampin nor cycloheximide had any effect on the three enzymes. RNA polymerase was isolated from three stages of the diploid life cycle: the hyphal growth stage, mycelia in the process of forming sporangia, and the mitospores. The same three enzyme species could be resolved from each stage. Thus, there is no evidence from this work that RNA polymerase plays a major role in the control of development.