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At least 199 records · Page 11Linked to original sources
PubMed1980

Characterization of promoter-cloning plasmids: analysis of operon structure in the rif region of Escherichia coli and isolation of an enhanced internal promoter mutant.

Using the promotor-cloning vehicle described by An and Friesen (J. Bacteriol. 140:400-410, 1979), Escherichia coli chromosomal deoxyribonucleic acid fragments derived from the lambda drifd18 transducing phage were cloned in one of several unique restriction endonuclease sites adjacent to tetracycline(tet) genes that lack their own promotor. One of these plasmids has been used to isolate nine variants having mutations that lie in a putative internal promoter which is located between rplL and rpoB. Deoxyribonucleic acid sequence analysis revealed that, in all nine mutants, a single base change, C to T, in the ribonucleic acid polymerase recognition site led to a large increase in promoter activity. Analysis of a variety of plasmids in which tet is fused to various promoters yielded the following results: (i) rplK and rplA, genes for ribosomal protein L11 and L1, respectively, were cotranscribed from a common promoter located upstream from rplK; (ii) there was a strong promoter in the region between the rplKA operon and rplJ, the gene for ribosomal protein L10; (iii) an attenuator region was located between rplL, the gene for ribosomal protein L12, and rpoB, the gene for ribonucleic acid polymerase subunit beta; (iv) transcription terminated immediately after rpoC, the gene for ribonucleic acid polymerase subunit beta'; (v) a gene coding for unknown protein U, which is located between tufB and the rplKA operon, had its own promoter; (vi) the tufB gene was separated from all of the genes described above and had its own promoter.

Bacterial Proteins↗
PubMed1984

Order of ribosomal protein genes in the Rif cluster of Bacillus subtilis is identical to that of Escherichia coli.

Mutants of Bacillus subtilis with electrophoretic variants of ribosomal protein L1, L5, L9, or L11 were used to determine the order of the genes for these proteins by transformation experiments. The proteins are homologous with Escherichia coli proteins L1, L10, L12, and L11, respectively; using the gene locus designations based on this correspondence, we determined the order of the loci to be cysA-rplK-rplA-rplJ-rplL-rpoB. The order of the last five loci was identical to that of E. coli.

Bacillus subtilis↗
PubMed1998

Sir proteins, Rif proteins, and Cdc13p bind Saccharomyces telomeres in vivo.

Although a surprisingly large number of genes affect yeast telomeres, in most cases it is not known if their products act directly or indirectly. We describe a one-hybrid assay for telomere binding proteins and use it to establish that six proteins that affect telomere structure or function but which had not been shown previously to bind telomeres in vivo are indeed telomere binding proteins. A promoter-defective allele of HIS3 was placed adjacent to a chromosomal telomere. Candidate proteins fused to a transcriptional activation domain were tested for the ability to activate transcription of the telomere-linked HIS3 gene. Using this system, Rif1p, Rif2p, Sir2p, Sir3p, Sir4p, and Cdc13p were found to be in vivo telomere binding proteins. None of the proteins activated the same reporter gene when it was at an internal site on the chromosome. Moreover, Cdc13p did not activate the reporter gene when it was adjacent to an internal tract of telomeric sequence, indicating that Cdc13p binding was telomere limited in vivo. The amino-terminal 20% of Cdc13p was sufficient to target Cdc13p to a telomere, suggesting that its DNA binding domain was within this portion of the protein. Rap1p, Rif1p, Rif2p, Sir4p, and Cdc13p activated the telomeric reporter gene in a strain lacking Sir3p, which is essential for telomere position effect (TPE). Thus, the telomeric association of these proteins did not require any of the chromatin features necessary for TPE. The data support models in which the telomere acts as an initiation site for TPE by recruiting silencing proteins to the chromosome end.

Binding Sites↗
PubMed1990

Cytotoxicity of lonidamine alone and in combination with other drugs against murine RIF-1 and human HT1080 cells in vitro.

Lonidamine is an agent that is reported to inhibit recovery from potentially lethal damage. By itself, it has only mild anticancer activity. We have examined the ability of lonidamine to enhance the cytotoxicity of several drugs against a mouse and a human fibrosarcoma cell line in vitro. By itself, lonidamine showed only a limited cytotoxic effect with drug exposure up to 100 micrograms/ml and 24-h duration. Lower concentrations and shorter term exposures were not toxic to either of these tumor cell lines. When tested against the mouse line, the cytotoxicity of 5-fluorouracil, methotrexate, and etoposide was enhanced by lonidamine if the latter drug was given either before or after the exposure of the cells to the cytotoxic agents. For cisplatinum, bleomycin, mitomycin C, doxorubicin, and Actinomycin D, cytotoxicity was also enhanced, but only if lonidamine followed the other agents. In contrast, potentiation of 1,3-bis(2-chloroethyl)-1-nitrosourea toxicity was maximum when lonidamine preceded the nitrosourea. The human cells were more resistant to lonidamine and to the combination treatments than were the mouse cells. Nevertheless, substantial enhancement was seen particularly for cisplatin and mitomycin C. We examined in more detail the enhancement of cisplatin. Maximum interaction was obtained when lonidamine was given immediately following (or in conjunction with) the platinum agent. Our results suggest that lonidamine enhances the effects of several other agents in a time- and concentration-dependent manner and indicate a potential usefulness for lonidamine in multidrug therapy.

Animals↗
PubMed1988

[Stability of Shigella flexneri attenuated strain 2A 77 ADE- RIF-r after cultivation in a fermenter and lyophilization].

The method for the cultivation of S. flexneri attenuated strain 2a 77 ade- rifr in a fermenter with the use of casein fermentative broth containing 200-250 mg% of amino nitrogen has been developed. No changes in the properties of the initial strain have been found after its cultivation in a fermenter or after the lyophilization of the cultures grown in a fermenter. After cultivation in casein fermentative broth with 100 mg% of amino nitrogen the presence of S-R dissociation has been established, the S colonies having the properties of the initial strain. The reversion of the R colonies to prototrophism in adenine and differences in the level of their resistance to rifampicin are observed. The study of the plasmid profile of the initial strain and its ade+ revertants has revealed the disappearance of plasmids with a molecular weight of 140 MD in these revertants. All clones under study (ade+ and ade-) show negative results in the keratoconjunctival test. The conditions of cultivation and the causes of reversion are discussed.

Fermentation↗
PubMedDate not supplied

[Characterization of a Rif-R population of Bacillus anthracis].

Formation of spontaneous RifR mutants was detected in the populations of various strains of Bacillus anthracis (STI-1, Sterne and CH-7) at a rate of 10(-8) per 1 CFU. The levels of the rifampicin resistance in the mutants were different, the MIC ranged from 16 to 512 micrograms/ml. The clones of the RifR population of the virulent strain CH-7 were heterogeneous in the morphological properties of the colonies and cells, the capacity for the synthesis of the toxin and capsule, the sporulation and virulence. The heterogeneity did not correlate with the levels of the antibiotic resistance. Among the clones of the RifR population there were detected deletion variants by the capacity for the synthesis of the toxin and capsule along with the complete ones. The rifampicin therapy of the infection caused by the complete clone was not efficient. The RifR mutation in B. anthracis did not result in cross resistance to penicillins, cephalosporins, tetracyclines, aminoglycosides, macrolides and chloramphenicol.

Bacillus anthracis↗
PubMed1999

Stability of rifampicin in dissolution medium in presence of isoniazid.

Rifampicin (RIF) hydrolyzes in acidic medium to form insoluble and poorly absorbed 3-Formyl rifamycin SV (3-FRSV). This study describes development of two principally different methods, Dual Wavelength UV-Vis. spectrophotometry (DW spectrophotometry) and HPTLC, to determine 3-FRSV in presence of RIF. Using DW spectrophotometry, RIF was estimated by using wavelengths 475.0 and 507.0 nm and 3-FRSV was estimated using 457.0 and 492.0 nm. In HPTLC method, a mixture of chloroform:methanol:water (80:20:2.5 v/v) was used as the mobile phase to resolve 3-FRSV from RIF and 3-FRSV was quantified at 333 nm. The linearity range for 3-FRSV was 2-10 microg/ml and 50-250 ng/spot for DW spectrophotometric method and HPTLC method, respectively, and 5-50 microg/ml for RIF using DW spectrophotometric method. Both the methods were found to be specific, accurate and reproducible. The proposed methods were successfully applied to determine the rate of degradation of RIF to 3-FRSV in dissolution medium (0.1 N HCl) and also in presence of isoniazid (INH). The rate of degradation of RIF in presence of INH was almost two times more than that of RIF alone. These methods were utilized to study the stability of RIF in market formulations of RIF and RIF with INH in dissolution medium. It has been observed that RIF degrades by 12.4% to form 3-FRSV (RIF formulations) while in presence of INH the degradation is catalyzed to about 21.5% (RIF+INH formulations), in 45 min. Thus, lower concentration of RIF may be available for absorption leading to poor bioavailability of RIF from combination dosage forms (RIF+INH) as compared to formulations containing only RIF. It is proposed that specific analytical method should be used to measure RIF in presence of 3-FRSV in a dissolution study.

Antitubercular Agents↗
PubMed2002

Genetic and physiological characterization of rpoB mutations that activate antibiotic production in Streptomyces lividans.

Antibiotic production in Streptomyces lividans can be activated by introducing certain mutations (rif) into the rpoB gene that confer resistance to rifampicin. Working with the most typical (rif-17) mutant strain, KO-417, the rif-17 mutation was characterized. The rif-17 mutation was shown to be responsible for activating antibiotic production and for reducing the growth rate of strain KO-417, as demonstrated by gene-replacement experiments. Gene-expression analysis revealed that introduction of rif into S. lividans elevates expression of the pathway-specific regulatory gene actII-ORF4 to nearly the same level seen in Streptomyces coelicolor. The rif effect on antibiotic production was still evident in the genetic background of relC, indicating that the rif mutation can provoke its effect without depending on ppGpp. Accompanying the restoration of antibiotic production, rif mutants also exhibited a lower rate of RNA synthesis compared to the parental strain when grown in a nutritionally rich medium, suggesting that the mutant RNA polymerases may behave like 'stringent' RNA polymerases. These results indicate that the rif mutation can alter the gene-expression pattern independent of ppGpp. The impaired growth of strain KO-417 (rif-17) was largely restored by introducing the second rif mutation (rif-18) just adjacent to the rif-17 position. Proteome analysis using two-dimensional PAGE revealed that the rif mutant strain KO-418 (rif-17 rif-18) displayed a temporal burst of expression especially of two enzymes, glutamine synthetase (type II) and oxidoreductase, during the late growth phase.

Amino Acids↗