RESUMO
The action of methoxyamine (MA) on B. subtilis transforming DNA (50 degrees C, pH 4,5 and 6,0, 1 M MA) was studied. The rate of cytosine residues modification in DNA is 250 times less than in monomer (rate constants for DNA are 1,5 X 10(-1) min-1 at pH 4,5, and 2,5 X 10(-6) min-1 in the first 300 hours of treatment at pH 6,0). At pH 4,5 the rates of cytosine (I) conversion into N4-methoxycytosine (II) and into 6-methoxyamino-5,6-dihydro-N4-methoxycytosine (III) are constant (II/III ratio is about 2,1). At pH 6,0 the II/III ratio smoothly increases from 1,0 to 1,6 (200 and 900 hours of treatment) due to a decrease in the product III accumulation rate. The frequency of MA-induced mutations shows a bell-shaped dependence on time with maxima (approximately 10%) at 80 (pH 4,5) and 500 (pH 6,0) hours of treatment. In both cases approximately 10% of cytosine residues are modified. These results suggest that either compound III is efficiently removed from the transforming DNA, or its presence does not arrest the DNA replication.
Assuntos
Bacillus subtilis/genética , DNA Bacteriano/genética , Hidroxilaminas/farmacologia , Transformação Bacteriana/efeitos dos fármacos , Composição de Bases/efeitos dos fármacos , Hidroxilamina , MutaçãoRESUMO
The mutagenic effect of O-methylhydroxylamine (OMHA) on transforming DNA of Bacillus subtilis was studied. In accordance with the earlier reported chemical and functional data, the mutagenic effect was observed at 4.5 and 6.0 pH. An increase in pH caused a decrease in the rate of mutagenesis, though the maximal level of mutagenesis was equal at both values of pH. The results obtained with recipients defective in the system of UV-repair revealed that both products of reaction of OMHA with the cytosine-base of DNA, N4-metoxycytidine and N4-metoxy-6-metoxyamino-5,6-dihydrocytidine, are effectively eliminated through the system of UV repair.
Assuntos
Bacillus subtilis/genética , DNA Bacteriano/genética , Hidroxilaminas/farmacologia , Mutagênicos/farmacologia , Transformação Bacteriana/efeitos dos fármacos , Bacillus subtilis/efeitos dos fármacos , Replicação do DNA/efeitos dos fármacos , Concentração de Íons de Hidrogênio , Mutação , Temperatura , Fatores de TempoRESUMO
Regulatory markers of ribC group were located on the chromosome of Bacillus subtilis by means of genetic transformation. Markers of this group controlling the regulation of riboflavin biosynthesis were mapped between markers of resistance to acriflavin and streptomycin (strC group). The value of cotransfer index between acriflavin-resistance markers and ribC markers was found to be 26--32%. Acriflavin inhibits the riboflavin biosynthesis. The level of inhibition depends on the genotype of riboflavin-producing strains, while the inhibition of the cell growth does not depend on it.
