The secondary structure of bacteriophage DNA in situ

Conversion of non‐covalent interactions in nucleoproteins into covalent bonds: UV‐induced formation of polynucleotide—protein crosslinks in bacteriophage Sd virions

“…Kisseleva. Phage was disrupted by heating for 30 min at 707C [15]. The phage concentration was determined as the DNA content which was assayed by the content of phosphorus.…”

“…Among the underlying reactions could be the interactions of the excited uracil and thymine nuclei with amino acid residues [7][8][9][10][11][12][13][14]. Strong nucleophilic agents are also known to induce crosslinks in viral nucleoproteins, involving cytosines driven out of the DNA double helix due to specific interactions with phage proteins [15][16][17] (see scheme 1).…”

“…These results imply that not only thymine and uracil but also cytosine nuclei involved in noncovalent interaction with proteins would be the subject of crosslinkage upon UV-irradiation of nucleoproteins, according to the above scheme. The involvement of pyrimidine bases in higher structures results in the lowering of the rate of their reaction with nucleophilic agents by more than two orders of magnitude [15,[20][21][22], but has a relatively small effect on the quantum yield of UV-induced hydration [23][24][25]. This fact as well as the possibility of covalent linkage in other types of polynucleotide-protein interactions makes the UV-induced crosslinks an important tool for the study of nucleoprotein structure.…”

“…On the basis of the above rationale we have studied the induction by UV of crosslinks in bacteriophage Sd; previously this phage had been used for the investigation of crosslinkage induced by nucleophilic agents [15][16][17].…”