The effect of rifamycin on RNA synthesis in the rat liver mitochondria

Variations in host defence mechanisms and blastogenesis in chickens and mice after rifamycin treatments

The immunobiological effect of rifamycins on different experimental models has been comparatively studied in chickens and mice using cyclophosphamide as a reference immunosuppressive agent. "In vivo" treatments with rifampicin and rifamycin SV diminished interferon levels in chickens and mice up to two hours after virus challenge. Mitogen induced blastogenesis was significantly depressed by either "in vivo" (5-50 mg/kg) or "in vitro" (5-20 micrograms/ml) drug treatments, although the activation of B lymphocytes was more easily inhibited than that of T lymphocytes. Primary anti-SRBC immune responses suffered a similar immune suppressive action by rifamycin treatments "in vivo". In every case, cyclophosphamide (10-20 micrograms/ml "in vitro" and 25 mg/kg "in vivo") proved to be the most active immunosuppressant. On the other hand, a remarkable parallelism in the effect of rifamycins in chickens and mice was observed in all the experimental systems used.

Detection of [3H]cyclic AMP in the transcription complex of rat liver mitochondria

By equilibrium ultracentrifugation and electrophoresis in agarose gel data were obtained on the binding of [3H]cyclic adenosine monophosphate ([3H]cAMP) to the transcriptional complex of mitochondria with the density 1.825 g/ml in CsCl ethydium bromide. Treatment of the complex with RNase, DNase and pronase change the density of [3H]cAMP bound material; rifampicin prevents detection of [3H]cAMP. Study of inner membrane lysates showed that [3H]cAMP is bound to structures active in RNA and protein synthesis in mitochondria. The conclusion is made that cAMP is involved in formation of the transcriptional complex much as it is involved in initiation of transcription in bacterial operons.

The isolation and properties of a DNA-directed RNA polymerase from yeast mitochondria

A method is described for the rapid isolation of yeast mitochondrial DNA-directed RNA polymerase. The enzyme obtained had a specific activity of 1.56 nmol UMP incorporated per mg protein in 20 min at 37 degrees C, and is some 95% pure. This purified enzyme upon polyacrylamide gel elctrophoresis consists of a single polypeptide of 68 000 mol. wt. However, the enzyme forms aggregates easily which are affected by ionic strength, an increase decreasing the apparent molecular weight of the aggregates. This property also explains the presence of two peaks of activity upon DEAE-cellulose chromatography. The purified enzyme is still sensitive to rifamycin and to a number of rifamycin derivatives. The enzyme's sensitivity to rifamycin and rifamycin derivatives was compared with Escherichia coli and yeast nuclear RNA polymerases.

Purification and properties of DNA-dependent RNA polymerase from Mycobacterium tuberculosis H37RV

RNA polymerase (nucleosidetriphosphate: RNA nucleotidyltransferase DNA-dependent), EC 2.7.7.6) was purified approximately 200 fold from Mycobacterium tuberculosis H37RV cells. The purified enzyme has a molecular weight of about 330 000-350 000 and is composed of four subunits. The subunits beta', beta and sigma have molecular weights different from those of Escherichia coli polymerase; the fourth, alpha subunit has a similar weight. The purified enzyme is a thousand-fold more sensitive to rifampicin, a potent antitubercular drug than the E. coli RNA polymerase, probably because of the difference in the beta subunits. This, with other data presented in this paper, indicate that the RNA polymerase of M. tuberculosis differs in its properties from that of E. coli.

In vitro DNA and RNA synthesis by human platelets

In vitro incorporation of [Me-3H] thymidine and [5-3H] uridine into human platelets was demonstrated. Thymidine incorporation was inhibited by three specific inhibitors of DNA synthesis: hydroxyurea, cytosine arabinoside and daunomycin. The effect was dose-dependent. Uridine uptake by platelets was found to be inhibited by specific inhibitors of RNA synthesis such as actinomycin D, rifampicin and vincristine, the effect of actinomycin D being dose dependent. The drug also led to a time-dependent inhibition of protein synthesis when preincubated with platelets. The platelet RNA profile on polyacrylamide gel was demonstrated to be similar to that of embryonic mouse erythroblast RNA. Synthesis of all three fractions, 28 S, 18 S and 4 S, was inhibited by actinomycin D. These findings show that human platelets are capable of DNA and RNA synthesis, and that these activities play a role in controlling protein synthesis in these cells. Detectable amounts of DNA have been found in whole human platelets, and in isolated mitochondria derived from these cells. Isolated platelet mitochondria incorporated [3H] thymidine and [3H] uridine into their macromolecules. These activities were inhibited by daunomycin and by both rifampicin and actinomycin D, respectively. These results support the assumption that DNA and RNA synthesis found in intact cell preparations takes place most probably in platelet mitochondria.

Migration of ribosomes along the axons of the chick visual pathway

The axoplasmic migration of ribosomes has been detected in the visual system of the chick. Monocular injection of radioactive uridine or an amino acid mixture was followed by sedimentation analysis in sucrose or cesium sulfate density gradients, of ribosomes prepared from the retinae of injected eyes and the left and right optic lobes. By this means both RNA and protein components of ribosomes were found to migrate from the retina to the innervated contralateral optic lobe. Following denervation of the distal nerve segment by eye removal, the stability of the transported RNA was reduced, suggesting its presynaptic location. The transport of RNA was not significantly imparied by intraocular injection of inhibitors of informational RNA or mitochondrial RNA synthesis prior to injection of radioactive uridine but was depressed by a low dose of actinomycin D.

Immunological and chemotherapeutic prevention and control of oncogenic viruses

Computed tomographic (CT) and surgical findings were correlated retrospectively in 51 patients with preoperative diagnoses of prolactin-secreting pituitary microadenomas. Twenty-four had microadenomas at surgery. Twenty-eight had identifiable discrete lesions. Of these, 18 had microadenomas and 10 did not; these two groups could not be distinguished reliably. Six patients with proven microadenomas had normal CT scans. Focal hypodense lesions, sellar floor erosion, infundibulum displacement, gland height greater than 8 mm, and an abnormal diaphragma sellae configuration are neither sensitive nor specific findings of microadenoma. A significant number of patients with proven microadenomas had few or none of these abnormalities. Thus, recognition of prolactin microadenoma is seldom possible by CT alone, even with high-resolution direct coronal imaging.

Partial purification of mitochondrial RNA polymerase from rat liver

Mitochondrial RNA polymerase activity from rat liver has previously been demonstrated in intact organelles. This activity has now been solubilized, partially purified, and shown to be a true polymerase, free of nuclease. The enzyme is derived from mitochondria and is not from contaminating bacteria or nuclear components. The enzyme is distinguished from its nuclear counterparts by its behavior on ammonium sulfate fractionation and lack of inhibition by alpha-amanitin. Rifamycin inhibits the crude enzyme, but only inconsistently inhibits the more purified preparation.

Inhibition of poxvirus maturation by rifamycin derivatives and related compounds

The effect of a number of rifamycin derivatives and related compounds on the reversibility of the rifampin-induced virus maturation block was studied by using BHK-21 cells infected with vaccinia virus. All of the derivatives of 3-formyl rifamycin SV maintained this block, the required concentration varying from 100 to 1,000 mug/ml. These compounds vary only in the nature of the side-chain attached to the 3C atom on the naphthohydroquinone moiety; no obvious correlation between the nature of this side-chain and antiviral activity was found. Streptovaricin complex and tolypomycin R also maintained the maturation block; tolypomycin also produced marked alterations in the appearance of the viroplasm contained in rifampin-induced inclusions and immature virus particles.

[The effect of rifampicin on the RNA- and protein synthesis as well as on the morphogenesis and on the chlorophyll content of nucleate and anucleate cells of Acetabularia]

Rifampicin (10μg/ml) strongly inhibits the incorporation of [5-(3)H]-uridine into the chloroplast RNA of anucleate cells of the green alga Acetabularia mediterranea, whereas incorporation into nuclear RNA is hardly affected.Furthermore, at a concentration range of 1-10[Symbol: see text]g/ml rifampicin has only a small effect on stalk- and cap formation in nucleate posterior parts of the stalk. As has already been shown, the morphogenesis of such cell segments depends on the synthesis of new RNA in the nucleus. Similarly rifampicin only slightly inhibits the synthesis of the enzyme UDPG-pyrophosphorylase, which is coded by nuclear DNA.These slight inhibitions are interpreted as secondary effects arising from a blockage of plastid RNA synthesis, since both nucleate and anucleate cells respond in a similar manner and to the same degree.In contrast the increase in the chlorophyll content in nucleate and anucleate cells is severely impaired by the antibiotic. These findings indicate that the nucleus and the plastids contain different DNA-dependent RNA-polymerases.

DNA-dependent RNA polymerase from yeast mitochondria

The DNA-dependent RNA polymerase present in the mitochondria of Saccharomyces cerevisiae has been solubilized using a 0.5 M KCI solution, and the soluble enzyme has been purified. Two forms of mitochondrial enzyme were obtained; they differ in their template specificity and metal-ion dependency. The mitochondrial RNA polymerase also differs from enzyme obtained from the nucleus with respect to antibiotic sensitivity and template specificity. Only the nuclear enzyme is sensitive to alpha-amanitin inhibition. The relative activities of the isolated nuclear and mitochondrial polymerases toward their homologous DNAs are consistent with their in vivo functions. The possibilities of bacterial- and nuclear-enzyme contamination of the mitochondrial enzyme preparation have been ruled out. RNA polymerase activity in two petite mutants has been studied. Isolated mitochondria from a petite mutant with no detectable mitochondrial DNA has greatly diminished mitochondrial DNA-dependent RNA polymerase activity, while a petite mutant with only a small change in mitochondrial DNA base composition has normal amounts of enzyme.