EFFECTS OF AMINOGLYCOSIDE ANTIBIOTICS ON INITIATION OF VIRAL RNA-DIRECTED PROTEIN SYNTHESIS

Abstract

Streptomycin, kanamycin, gentamicin, and kasugamycin were observed to inhibit f2 phage RNA-directed protein synthesis in an Escherichia coli system. When the reaction mixture was allowed to translate viral RNA for 5 minutes before addition of antibiotics, the synthesis was completely blocked by streptomycin or thiopeptin; but significant synthesis continued in the presence of kasugamycin, kanamycin and gentamicin. The results suggested that kasugamycin, kanamycin and gentamicin may inhibit initiation, and streptomycin may interfere with both chain initiation and elongation. Thiopeptin may affect chain elongation. The binding of fMet-tRNA to 70S ribosomes in the presence of f2 RNA was inhibited by streptomycin, kanamycin, gentamicin, and kasugamycin. The release of fMet-tRNA from the initiation complex was significantly induced by streptomycin, kanamycin, and gentamicin; but not by kasugamycin. The results indicated that the inhibition by kasugamycin of 30S initiation complex formation may result in the apparent inhibition of 70S initiation complex formation. And the apparent inhibition by streptomycin, kanamycin, and gentamicin of 70S initiation complex formation may be caused by breakdown of the complex and inhibition of ribosomal dissociation. The effects of streptomycin, kanamycin, and gentamicin were more significant with the initiation complex formed on washed 70S ribosomes than with the complex formed on unwashed 70S ribosomes. The ribosomal proteins washed out in 1 M NH₄Cl protected the target sites from the antibiotic actions. The T factor- and messenger-dependent binding of Ala-tRNA to the ribosomes was significantly affected by streptomycin, but not by kanamycin, gentamicin, and kasugamycin.