The secondary structure of bacteriophage DNA in situ: III. Reaction of S d phage with O-methylhydroxylamine

Abstract

Cytosine nuclei in denatured DNA and in DNA inside the S d phage readily react with O-methylhydroxylamine, whereas no reaction with native DNA is observed under the same experimental conditions. In the intraphage DNA, about 20% of cytosine participates in the reaction, the rate of modification of cytosine being close to that of modification of cytosine nuclei in monomers. “Reactive” cytosine of the intraphage DNA is likely to be localised in the sites having no base stacking. Comparison of the results obtained by different methods applied to the study of the course of modification leads to the conclusion that the main product of interaction between O-methylhydroxylamine and the cytosine nucleus in intraphage DNA is N (4)-methoxy 6-methoxyamino-5,6-dihydro-cytosine nuclei among the final products. The absence of N (4)-methoxycytosine nucleus testifies to the fact that the C (2) N (3) C (4) NH 2 group of the cytosine nuclei probably is not free, as is the case with monomers and denatured DNA, but evidently participates in the interaction with the phage protein. In the early stages of the reaction between O-methylhydroxylamine and intraphage DNA, there appears a new intermediate product—so-called derivative V.