BACTERIAL RIBONUCLEASE - MUTAGENIC EFFECT IN MICROBIAL TEST-SYSTEMS

Pure enzyme samples of ribonuclease from Bacillus intermedius 7P (know n commercially as 'binase') were investigated for genotoxicity in four microbial tests: the Ames plate incorporation method, Ara(R)-assay; t he prophage induction test; and the DNA-repair test. The weak mutageni c effect of binase at high concentrations (0.1 mg/plate, 1 mg/plate) w as established by induction of forward Ara(R)-mutations and histidine- reverse mutations (both frameshift mutations and base pair substitutio n), Metabolic activation with rat or chicken liver, human placenta or plant (from tulip bulbs) microsomal fractions in vitro was seen to abo lish the binase mutagenicity. Bacillus intermedius 7P ribonuclease app ears to possess DNA damaging activity in uvrA(-) and polA(-) mutants, but not in the recA-deficient Escherichia coil strain, and exhibits an induction of recA-dependent mutagenesis detected by the 8-fold increa se of the prophage-induction level in lysogenic Bacillus subtilis cult ure and by the 9-fold increase of this level in the Streptomyces laven dulae 3 lysogenic strain. The importance of the roles of both of enzym e catalytic activity and native structure is emphasized. A proposed me chanism for exogenous ribonuclease action is discussed. Bacillus inter medius 7P ribonuclease probably does not act as a direct genotoxic age nt interacting with DNA, but could provoke nucleotide imbalance throug h its catalytic action on membrane-associated RNAs, which results in a lteration of DNA replication and, as a consequence, in recA-dependent mutagenesis.