Interaction of granaticin B with the transcription system of Bacillus subtilis

Inhibitors of aminoacyl-tRNA synthetases as novel anti-infectives

Resistance to existing antibiotics has emerged as a major problem in healthcare. Novel antibiotics for which bacteria have not yet acquired resistance need to be developed to combat drug-resistant pathogens. Aminoacyl-tRNA synthetases are leading targets for novel anti-infectives. The validation of aminoacyl-tRNA synthetases as drug targets for anti-infectives has been established in an animal system. Using several conceptually distinct approaches, new inhibitors of synthetases have been developed as drug prototypes.

Effect of granaticin on the activity of DNA-directed RNA polymerase from Streptomyces granaticolor

DNA-directed RNA polymerase was isolated from wild-type and mutant (asporogenic and granaticin overproducing) Streptomyces granaticolor. The effect of granaticin on the enzyme activity was compared with that of standard transcription inhibitors, rifampicin and rifamycin SV and shown to be zero.

Mechanism of action of granaticin: inhibition of ribosomal RNA maturation and cell cycle specificity

Granaticin, an antibiotic produced by Streptomyces species was found to be cytotoxic (ED50 3.2 microgram/ml) against human oral epidermoid carcinoma (KB) cells. AT ED50 concentrations RNA synthesis was inhibited to the greatest extent. Prelabeling of RNA in KB cells, followed by addition of granaticin (2.13 microgram/ml) showed that ribosomal RNA maturation was inhibited. The inhibition of the formation of functional ribosomal RNA was determined by sucrose gradient centrifugation and showed that the accumulation of 45S preribosomal RNA was dependent on granaticin concentration and on the time granaticin was in contact with the KB cells. The effect of granaticin (6.3 microgram/ml) on KB cells in the different cell cycle phases showed preferential inhibition (93%) of cell survival in the G2 phase. However, RNA synthesis was only 20% inhibited by granaticin in KB cells in the G2 phase. From these results, it was concluded that ribosomal RNA maturation was not the only site of action of granaticin toxicity.