[Interaction between sodium bisulfite and bacteriophage SD DNA]

Area of Science:

• Molecular Biology
• Virology
• Biochemistry

Background:

• Understanding viral nucleoprotein structure is crucial for virology.
• Phage DNA contains cytosine residues that can interact with chemical agents.
• Sodium bisulfite is a reagent used to probe DNA structure.

Purpose of the Study:

• To investigate the interaction between sodium bisulfite and cytosine in phage SD DNA.
• To elucidate the structure of viral nucleoprotein through chemical modification.
• To identify the products of bisulfite modification and their implications for DNA-protein interactions.

Main Methods:

• Bisulfite modification of intraphage DNA in phage SD.
• Perchloric acid hydrolysis of modified phage DNA.
• Mild destruction of modified phage in various buffer conditions (NaCl, Tris-HCl, phosphate).
• Heating modified phage at 70°C in phosphate buffer.
• Viscosometry and Cs2SO4 density gradient centrifugation.

Main Results:

• Bisulfite modification led to an 18% decrease in cytosine and the formation of cytosyl amino acids (cytosyl lysine).
• These products were observed only after acidic hydrolysis or heating in phosphate buffer, not after mild destruction in NaCl or Tris-HCl.
• The formation of nucleotide-protein covalent cross-links (cytosyl amino acids) explains observed changes in viscosity and density.
• An intermediate product (product VII), a C5--C6-dihydro-C6-sulfopyrimidine with a screened amino group, is proposed to form in situ.

Conclusions:

• Sodium bisulfite reacts with cytosine in phage SD DNA, forming covalent cross-links with proteins.
• Phosphate ions and heat stabilize these cross-links, suggesting their role in viral nucleoprotein structure.
• The proposed intermediate product (product VII) is essential for understanding the reaction mechanism and its dependence on environmental conditions.