ABSTRACT
With biologically active DNA of the bacteriophage phi X174, both single and double-stranded, some physico-chemical and biological parameters of the depurination reaction are studied. It is shown that in single-stranded DNA each apurinic site is lethal, while in double-stranded RFI-DNA only about 5% of these sites are lethal. Furthermore it is concluded that the apurinic sites are formed at different rates in single- and double-stranded DNA and also the conversion into breaks of the apurinic sites is different for both forms of DNA.
Subject(s)
Bacteriophage phi X 174/analysis , DNA, Single-Stranded , DNA, Viral , Apurinic Acid , Hydrogen-Ion Concentration , KineticsABSTRACT
Gamma-ray induced alkali-labile sites, which are converted into breaks by alkali or heat, are compared with apurinic sites in both single-stranded and phi X174RF-DNA. It is shown that the kinetics of the conversion into breaks are completely different for both sites. The conclusion is: the gamma-ray induced alkali-labile sites are not identical with apurinic or/and apyrimidinic sites.
Subject(s)
DNA, Single-Stranded/radiation effects , DNA, Viral/radiation effects , Alkalies , Bacteriophage phi X 174 , Gamma Rays , Purines , Sodium Hydroxide , Time FactorsABSTRACT
The effect of sulphydryl compounds on the induction of alkali-labile sites and on the contribution of such sites to the inactivation of single-stranded phi X174 DNA was studied. Cysteamine is capable of reacting with DNA radicals, thereby modifying the radiation damage in such a way that the induction of immediate and latent breaks is reduced. This depends on the pH of the solution. With cysteine only, a pH dependent protection, against lethal alkali-labile potential breaks could be observed. The damage other than breaks is not influenced by the presence of sulphydryl compounds.
Subject(s)
Bacteriophage phi X 174/radiation effects , DNA, Viral/radiation effects , Sulfhydryl Compounds/pharmacology , Alkalies/pharmacology , Bacteriophage phi X 174/drug effects , Cysteamine/pharmacology , Cysteine/pharmacology , DNA Repair , DNA, Single-Stranded/radiation effects , Hydrogen-Ion Concentration , Radiation-Protective Agents , TemperatureABSTRACT
Gamma-irradiation of double-stranded RF-DNA of bacteriophage phi X174 in aqueous solution in the presence of oxygen produces at least one type of alkali-labile site. It is lethal and gives rise to breaks by alkali and is identical with the damage which becomes manifest by post-irradiation heat treatment. The effect of alkali is dependent on temperature. Furthermore, the excision repair system is not involved in eliminating lethal nucleotide damage in RFI-DNA.
Subject(s)
DNA/radiation effects , Alkalies/pharmacology , Bacteriophage phi X 174/drug effects , DNA Repair , DNA, Single-Stranded , Dose-Response Relationship, Radiation , Gamma Rays , Oxygen , TemperatureABSTRACT
Single-stranded phiX174 DNA in aqueous solutions has been irradiated in the absence of oxygen, under conditions in which only H radicals react with the DNA. It was shown that H radical reactions result in breaks, which contribute approximately 10 per cent inactivation. Further, two types of alkali-labile sites are formed. One is lethal and gives rise to single-strand breaks by alkali and is most probably identical with post-irradiation heat damage and contributes about 33 per cent to the inactivation mentioned above. The other consists of non-lethal damage, partly dihydropyrimidine derivatives, and is converted to lethal damage by alkali. This follows from experiments in which the DNA was treated with osmium-tetroxide, which oxidizes thymine to 5,6-dihydroxy-dihydrothymine. Treatment with alkali of this DNA gives the same temperature dependence as found for the non-lethal alkali-labile sites in irradiated DNA. A similar temperature dependence is found for dihydrothymine and irradiated pyrimidines with alkali.
