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PubMed2000

Conformational changes in the ribosome induced by translational miscoding agents.

Ribosomes are dynamic complexes responsible for translating the genetic information encoded in mRNAs to proteins. The accuracy of this process is vital to the survival of an organism, and is often compromised by translational miscoding agents. Aminoglycosides are a group of miscoding agents that bind to the ribosome and reduce the fidelity of translation. Previous studies have shown that aminoglycosides alter the higher order structure of the ribosome. Here, we used a toeprinting assay to how that streptomycin, neomycin, kanamycin, gentamycin, and hygromycin B trigger conformational changes within Escherichia coli ribosome. Miscoding agents viomycin and 30% ethanol also cause similar structural changes within the ribosome. In contrast, antibiotics that do not cause miscoding, such as tetracycline, chloramphenicol, erythromycin, fusidic acid and spectinomycin, do not induce the conformational changes triggered by miscoding agents. Furthermore, ribosomes isolated from strains that are either streptomycin resistant or dependent for growth do not show these conformational changes in the presence of streptomycin. These results correlate structural changes in the ribosome induced by miscoding agents in vitro with their in vivo phenotype.

Anti-Bacterial Agents↗
PubMed1984

Effects of nephrotoxic compounds on active uptake of drugs in isolated renal tubules in rabbits.

The uptake of sulfonamides and phenolsulfonphthalein (PSP) was examined in vitro using isolated renal proximal tubule suspension, and the effects of nephrotoxic compounds on the uptake of sulfamethizole (SMZ) were studied. The uptake of SMZ and PSP was energy dependent and was inhibited competitively by iodopyracet (IP), which is transported actively by the p-aminohippurate mechanism. The uptake of sulfamethoxazole was also reduced by IP but that of sulfanilamide was negligible. The present results correspond well with those of in vitro experiments reported previously. Nephrotoxic compounds, mercuric chloride, neomycin, viomycin and kanamycin, decreased the uptake of SMZ non-competitively. The inhibitory action of the three antibiotics corresponds with in vivo potency, suggesting that this renal tubule preparation may provide a simple method for predicting the nephrotoxicity of drugs.

Animals↗
PubMed1990

A new liquid-phase enzyme immunoassay for rabbit IgM antibodies and its application for comparing the specificity of IgM and IgG antibodies contained in the same antiserum.

A new liquid-phase enzyme immunoassay (EIA) has been developed to compare the specificities of IgM and IgG antibodies when they are both present in the same serum sample and directed towards a simple hapten. The hapten viomycin (VM) was used as the model antigen and antibodies to VM were raised in rabbits. In the immunoassay VM, labelled with the enzyme galactosidase as marker (VM-GAL), was mixed with rabbit anti-VM serum. First IgM anti-VM antibodies bound to VM-GAL were precipitated with a guinea pig anti-rabbit IgM serum and galactosidase activity was measured in the precipitate. Then IgG anti-VM antibodies bound to VM-GAL were precipitated from the supernatant with a goat anti-rabbit IgG serum and enzyme activity was measured in this precipitate. The guinea pig anti-rabbit IgM and goat anti-rabbit IgG were specific for IgM and IgG respectively and did not appear to cross-react. Nine analogues of VM were used as inhibitors in this immunoassay to compare the specificities of IgM and IgG antibodies for determinants on VM. The results suggest that recognition of the fine structure of VM by IgM is less strict than recognition by IgG.

Animals↗
PubMed1994

Peptide antibiotics of the tuberactinomycin family as inhibitors of group I intron RNA splicing.

The tuberactinomycins are a group of cyclic peptide antibiotics, which are potent inhibitors of prokaryotic protein synthesis. We report the inhibitory effect of viomycin, di-beta-lysyl-capreomycin IIA and tuberactinomycin A on group I intron self-splicing. They compete with the guanosine cofactor for the G-binding site located in the conserved core of the intron. They are 100-fold more active than all other competitive inhibitors described so far (dGTP, arginine or streptomycin), inhibiting splicing at concentrations between 10 and 50 microM. Mutation of the G-binding site leads to partial resistance, and the inhibitory effect of these drugs is dependent on Mg2+ concentration. This suggests that the tuberactinomycins have more than one contact site with the intron RNA: via the G-binding site and via additional contacts with the RNA backbone. Positioning the tuberactinomycins in the three-dimensional model of the td intron core suggests that the charged lysyl side-chain (R1) is in contact with the backbone of the P1 helix. Structure/function analyses with various tuberactinomycin analogues with different activities confirm the involvement of this sidechain in inhibition of group I self-splicing. The demonstration of a new class of splicing inhibitors, the peptide antibiotics, illustrates how antibiotics may interact with catalytic RNA.

Bacteriophage T4↗
PubMed1992

Puromycin reaction of the A-site bound peptidyl-tRNA.

AcPhe2-tRNA(Phe) which appears in ribosomes after consecutive binding of AcPhe-tRNA(Phe) at the P sites and EF-Tu-directed binding of Phe-tRNA(Phe) at the A sites is able to react quantitatively with puromycin in the absence of EF-G. One could readily explain this fact to be the consequence of spontaneous translocation. However, a detailed study of kinetics of puromycin reaction carried out with the use of viomycin (inhibitor of translocation) and the P-site test revealed that, apart from spontaneous translocation, this peptidyl-tRNA could react with puromycin being located at the A site. This leads to the conclusion that the transpeptidation reaction triggers conformational changes in the A-site ribosomal complex bringing the 3'-end of a newly synthesized peptidyl-tRNA nearer to the peptidyl site of peptidyltransferase center. This is detected functionally as a highly pronounced ability of such a peptidyl-tRNA to react with puromycin.

Binding Sites↗
PubMed1985

The Streptomyces plasmid SCP2*: its functional analysis and development into useful cloning vectors.

Detailed restriction maps of the plasmid SCP2* and its deletion derivative pSCP103 were constructed. DNA fragments carrying hygromycin (Hyg), thiostrepton (Thio) or viomycin-resistance (VioR) determinants were inserted into pSCP103, and various segments were deleted from the resulting plasmids. Changes in plasmid phenotypes associated with these insertions and deletions allowed the localisation and characterisation of plasmid replication, stability, transfer and fertility functions. Several useful cloning vectors were constructed. They are able to maintain large (greater than 30 kb) DNA inserts, with stable inheritance at a low copy number (1-2 per chromosome) and without structural rearrangements, in Streptomyces hosts. The vectors have a broad host range in the genus Streptomyces. One of them (pIJ903) is a shuttle vector for Streptomyces and Escherichia coli.

Cinnamates↗
PubMed1986

A Bartter's-like syndrome from capreomycin, and a similar gentamicin tubulopathy.

Marked renal potassium and magnesium wasting, alkalosis, and a progressive increase in plasma renin and eventual hyperaldosteronemia developed during a 15-month course of in-hospital capreomycin therapy that was necessary for drug-resistant pulmonary tuberculosis. A prominent feature of the present case was renal chloride wasting, a feature of the capreomycin syndrome that has previously received little attention. Similar potentially life-threatening metabolic abnormalities, which resemble those found in Bartter's syndrome, can occur during prolonged therapy with the antibiotic gentamicin. In the present case, electrolyte abnormalities were unaffected by three days of indomethacin therapy but were partially corrected by large doses of spironolactone. Capreomycin, viomycin (an antibiotic closely related to capreomycin), and gentamicin are highly basic polypeptide antibiotics that may induce strikingly similar and potentially fatal syndromes of renal tubular dysfunction that can feature multiple electrolyte abnormalities.

Adult↗
PubMed1999

Depletion of Escherichia coli 4.5S RNA leads to an increase in the amount of protein elongation factor EF-G associated with ribosomes.

In Escherichia coli, 4.5S RNA is found in complexes with both protein translocation protein, Ffh (a bacterial homolog of mammalian SRP54) and protein synthesis elongation factor G (EF-G). To analyze the function of 4.5S RNA in translation, we initially assessed the sensitivity of the association of 4.5S RNA with the ribosome after treatment with antibiotics that affect various stages of protein synthesis. Fusidic acid and viomycin caused 4.5S RNA to cosediment with the 70S ribosomal fraction, indicating that 4.5S RNA enters the ribosome before ribosomal translocation and release of EF-G-GDP from the ribosome. On the other hand, depletion of 4.5S RNA led to the retention of a significant amount of EF-G on 70S ribosomes. In addition, 4.5S RNA shares a conserved decanucleotide sequence (58GAAGCAGCCA67) motif with the characterized EF-G-binding site at positions 1068-1077 on 23S RNA. We therefore examined by gel mobility-shift assay whether or not mutations in the domain-IV region of 4.5S RNA, including this conserved motif, disturb the binding of EF-G to 23S RNA. Any mutation at the C62, G64 or A67 residues within this motif abolished competition activity. Therefore, we propose that 4.5S RNA is concerned with the mode of association of EF-G with the ribosomes. Moreover, this function depends on the secondary structure of 4.5S RNA as well as a ten-base sequence conserved between the two RNAs.

Bacterial Proteins↗
PubMed1998

Antibacterial spectra of drugs used for chemotherapy of mycobacterial infections.

The mechanism of action of many antimycobacterial agents is poorly understood. To obtain preliminary information on whether the targets for some of these drugs might also occur in other bacteria, the in vitro activities of selected agents against Escherichia coli, Bacillus subtilis and Staphylococcus aureus were determined. Dapsone, p-aminosalicylic acid and thiacetazone failed to inhibit the above organisms (MIC values > 100 micrograms/ml) that may therefore lack targets for these drugs. Capreomycin, viomycin and clofazimine demonstrated activity against some of the organisms (MIC values < 100 micrograms/ml) suggesting that the targets of these drugs may not be restricted to mycobacterial species. The agents were all potent inhibitors of Mycobacterium bovis bacille Calmette-Guérin (MIC values 0.08-0.5 microgram/ml).

Aminosalicylic Acid↗
PubMed1979

Codon-anticodon interaction at the ribosomal P (peptidyl-tRNA)site.

A method for binding tRNA to ribosomes, introduced by Watanabe [Watanabe, S. (1972) J. Mol. Biol. 67, 443-457], permits nonenzymatic binding of N-acetyl-Phe-tRNA(Phe) to either the ribosomal aminoacyl-tRNA (A) or peptidyl-tRNA (P) site with almost 100% specificity. We used this method to analyze a possible codon-anticodon interaction at the P site for NH(2)-blocked aminoacyl-tRNA and deacylated tRNA. N-Acetyl-Phe-tRNA(Phe) bound only to the P site of poly(U)-programmed 70S ribosomes, not to poly(A)-programmed ribosomes. The reverse mRNA dependence was found for N-acetyl-Lys-tRNA(Lys). A series of purified deacylated tRNAs was analyzed in the poly(U) and poly(A) system for abilities to block P-site binding of N-acetyl-aminoacyl-tRNA and to direct the N-acetyl-aminoacyl-tRNA to the A site. Only the cognate tRNA was as effective as the bulk tRNA at a concentration of less than 1/20th that of bulk tRNA. tRNAs whose corresponding codons are identical or similar (same base character) in the first two codon positions showed a low but significant effect. The other noncognate tRNAs were unable to direct the NH(2)-blocked aminoacyl-tRNAs to the A site. Chlortetracycline interfered neither with the P-site binding of NH(2)-blocked aminoacyl-tRNA nor with the effects of deacylated tRNAs. Furthermore, the translocation blocker viomycin affected neither the binding to the A site nor that to the P site. These effects of both antibiotics indicate that both kinds of tRNA do not bind transiently in the A site before filling the P site and that codon-anticodon interaction takes place at the P site.

Anticodon↗
PubMed2003

Release of ribosome-bound ribosome recycling factor by elongation factor G.

Elongation factor G (EF-G) and ribosome recycling factor (RRF) disassemble post-termination complexes of ribosome, mRNA, and tRNA. RRF forms stable complexes with 70 S ribosomes and 50 S ribosomal subunits. Here, we show that EF-G releases RRF from 70 S ribosomal and model post-termination complexes but not from 50 S ribosomal subunit complexes. The release of bound RRF by EF-G is stimulated by GTP analogues. The EF-G-dependent release occurs in the presence of fusidic acid and viomycin. However, thiostrepton inhibits the release. RRF was shown to bind to EF-G-ribosome complexes in the presence of GTP with much weaker affinity, suggesting that EF-G may move RRF to this position during the release of RRF. On the other hand, RRF did not bind to EF-G-ribosome complexes with fusidic acid, suggesting that EF-G stabilized by fusidic acid does not represent the natural post-termination complex. In contrast, the complexes of ribosome, EF-G and thiostrepton could bind RRF, although with lower affinity. These results suggest that thiostrepton traps an intermediate complex having RRF on a position that clashes with the P/E site bound tRNA. Mutants of EF-G that are impaired for translocation fail to disassemble post-termination complexes and exhibit lower activity in releasing RRF. We propose that the release of ribosome-bound RRF by EF-G is required for post-termination complex disassembly. Before release from the ribosome, the position of RRF on the ribosome will change from the original A/P site to a new location that clashes with tRNA on the P/E site.

Dose-Response Relationship, Drug↗
PubMed1986

Analysis of the puromycin reaction. The ribosomal exclusion principle for AcPhe-tRNA binding re-examined.

The standard technique for determination of the ribosomal site location of bound tRNA, viz. the puromycin reaction, has been analyzed with regard to its applicability under tRNA saturation conditions. The criteria derived have been used to re-examine the exclusion principle for peptidyl-tRNA binding, which states that only one peptidyl-tRNA (AcPhe-tRNA) can be bound per ribosome although in principle two sites (A and P site) are available. The following results were obtained. The puromycin reaction is only appropriate for a site determination if the reaction conditions prevent one ribosome from performing more than one puromycin reaction. With an excess of AcPhe-tRNA over ribosomes, and in the absence of EF-G, this criterion is fulfilled at 0 degree C, where the P-site-bound material reacts with puromycin (quantitative reaction after 50 h), while the A-site-bound material does not. In contrast, at 37 degrees C the extent of the puromycin reaction can exceed the binding values by 2-4-fold ('repetitive reaction'). In the presence of EF-G a repetitive puromycin reaction is seen even at 0 degree C, i.e. EF-G can already promote a translocation reaction at 0 degree C. However, the extent of translocation becomes negligibly low for short incubation times (up to 60 min) at 0 degree C, if only catalytic amounts of EF-G are used. Using the criteria outlined above, the validity of the exclusion principle for Escherichia coli ribosomes was confirmed pursuing two different experimental strategies. Ribosomes were saturated with AcPhe-tRNA at one molecule per 70S ribosome, and a quantitative puromycin reaction demonstrated the exclusive P-site location of the AcPhe-tRNA. The same result was also found in the presence of viomycin, which blocks the translocation reaction. These findings also indicate that here nearly 100% of the ribosomes participate in AcPhe-tRNA binding to the P site. Precharging the P sites of 70S ribosomes with one Ac[14C]Phe-tRNA molecule per ribosome prevented additional Ac[3H]Phe-tRNA binding. In contrast, 70S particles carrying one molecule of [14C]tRNAPhe per ribosome were able to bind up to a further 0.64 molecule Ac[3H]Phe-tRNA per ribosome.

Binding Sites↗
PubMed1990

Cloning vectors derived from Streptomyces niveus plasmid pSN2.

Two high copy number, broad host range, general purpose cloning vectors, pLG5 and pLG10, derived from the unstable Streptomyces niveus plasmid pSN2 are described. pLG5 (5.5 kb) and pLG10 (6.5 kb) both carry the thiostrepton resistance (TsrR) and lethal zygosis (Ltz+) markers and have single cloning sites within a non-essential region and the tsr gene. pLG505 (7.4 kb) was constructed by cloning the viomycin resistance (vph) gene into the single BamHI site of pLG5 to give a further vector with insertion and replacement sites which inactivate either the TsrR or VioR functions.

Cloning, Molecular↗
PubMed2002

Transposition of Tn4560 of Streptomyces fradiae in Mycobacterium smegmatis.

Tn4560 (8.6 kb) was derived from Tn4556, a Tn3-like element from Streptomyces fradiae. It contains a viomycin resistance gene that has not been used previously for selection in mycobacteria. Tn4560, cloned in a Streptomyces plasmid, was introduced by electroporation into Mycobacterium smegmatis mc(2)155. Tn4560 transposed into the host genome: there was no obvious target sequence preference, and insertions were in or near several conserved open reading frames. The insertions were located far apart on different AseI macrorestriction fragments. Unexpectedly, the transposon delivery plasmid, pUC1169, derived from the Streptomyces multicopy plasmid pIJ101, replicated partially in M. smegmatis, but was lost spontaneously during subculture. Replication of pUC1169 probably contributed to the relatively high efficiency of Tn4560 delivery: up to 28% of the potential M. smegmatis transformants acquired a stable transposon insertion. The data indicated that Tn4560 may be useful for random mutagenesis of M. smegmatis.

Antibiotics, Antitubercular↗
PubMed1976

Altered ribosomes in antibiotic-resistant mutants of Mycobacterium smegmatis.

Two alleles for viomycin-capreomycin resistance (vic) in Mycobacterium smegmatis affect ribosome structures. One (vicA) affects a component of 50S subunits and the other (vicB) affects a component of 30S subunits. The locus for neomycin-kanamycin resistance (nek), which is linked to vicA and vicB, affects a component of 30S subunits. Although the erythromycin resistance locus (ery) is linked to vic and nek, no ribosomal alterations could be detected. Mutations at the streptomycin locus (str) not linked to vic and nek caused alterations of 30S subunits.

Anti-Bacterial Agents↗
PubMed1971

In vitro chemotherapeutic combinations against isoniazid-resistant Mycobacterium tuberculosis and Mycobacterium fortuitum.

It is an acceptable medical practice to use second-line antimycobacterial drugs in combination with isoniazid in treatment of isoniazid-resistant tuberculosis. Recent investigations have demonstrated the importance of determining chemotherapeutic interaction in instances of multiple antibiotic use. We studied the inhibitory effect of combinations of isoniazid with ethambutol, rifampin, ethionamide, cycloserine, viomycin, and kanamycin against three isoniazid-resistant strains of Mycobacterium tuberculosis and three strains of M. fortuitum. The isobologram technique with drug concentrations of 0.4 to 100 mug/ml was used. With the exception of single instances in which kanamycin plus isoniazid (M. tuberculosis strain 9999) and ethionamide plus isoniazid (M. fortuitum strain 2080) seemed to have a synergistic effect, neither synergy nor antagonism was noted for any of the combinations. These studies show that the combined use of isoniazid and a second line antimycobacterial agent results in vitro in indifferent inhibitory activity.

Antitubercular Agents↗
PubMed1998

Identification of the rrmA gene encoding the 23S rRNA m1G745 methyltransferase in Escherichia coli and characterization of an m1G745-deficient mutant.

An Escherichia coli mutant lacking the modified nucleotide m1G in rRNA has previously been isolated (G. R. Björk and L. A. Isaksson, J. Mol. Biol. 51:83-100, 1970). In this study, we localize the position of the m1G to nucleotide 745 in 23S rRNA and characterize a mutant deficient in this modification. This mutant shows a 40% decreased growth rate in rich media, a drastic reduction in loosely coupled ribosomes, a 20% decreased polypeptide chain elongation rate, and increased resistance to the ribosome binding antibiotic viomycin. The rrmA gene encoding 23S rRNA m1G745 methyltransferase was mapped to bp 1904000 on the E. coli chromosome and identified to be identical to the previously sequenced gene yebH.

Chromatography, High Pressure Liquid↗
PubMed1975

Investigations on in vitro survival and virulence of T. pallidum under aerobiosis.

Motility of pathogenic T. pallidum was maintained in aerobic in vitro cultures for several weeks using a special medium. The latter consisted of McCoy's 5a medium supplemented with glutathione, sodium pyruvate, HEPES buffer, gentamycin (garamycin), and fetal calf serum. The virulence of the organisms was lost in 5 to 6 days. No multiplication of the organisms was observed. Four antibiotics (viomycin, kanamycin, gentamycin (garamycin), and neomycin) were tested for their bactericidal action and possible toxicity to T. pallidum. Gentamycin proved to be superior to the other three antibiotics in being non-toxic to the treponemes and showing a possible stimulatory effect on their motility and longevity. Cultivation of T. pallidum in cultured cells in the presence of the enzymes, superoxide dismutase and catalase, in a special medium showed possibilities for future experimentation under monitored, reduced oxygen pressure with a continuous system to dismutate superoxide radicals.

Aerobiosis↗