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Packaging of DNA in bacteriophage Heads: Some considerations on energetics
Author(s) -
Riemer Steven C.,
Bloomfield Victor A.
Publication year - 1978
Publication title -
biopolymers
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.556
H-Index - 125
eISSN - 1097-0282
pISSN - 0006-3525
DOI - 10.1002/bip.1978.360170317
Subject(s) - chemistry , dna , spermidine , dna condensation , gibbs free energy , crystallography , bacteriophage , mole , putrescine , hydration energy , polyelectrolyte , thermodynamics , biochemistry , molecule , organic chemistry , polymer , enzyme , escherichia coli , transfection , physics , gene
We have made quantitative estimates of some of the energetic factors to be considered in packaging of double‐stranded DNA in virus particles. Numerical calculations were made using parameters appropriate for T4 bacteriophage. The unfavorable factors, and the Gibbs free energies per mole virus at 20°C associated with them, are bending, 1.5 × 10 3 kcal/mol; conformational restriction upon condensation, 5.1 × 10 2 kcal/mol; polyelectrolyte repulsion, 2.1 × 10 5 kcal/mol; and melting or kinking, 6.9 × 10 3 kcal/mol. These must be counterbalanced in the assembled phage by noncovalent bonding interactions between protein subunits in the phage‐head shell; by interactions between the DNA and polyvalent cations, especially putrescine and spermidine; nad perhaps by repulsive excluded volume and electrostatic interaction between the DNA and acidic polypeptides. Indeed, a rough estimate of the standard free energey of interaction between T4 DNA and the putrescine and spermidine contained in the head is ‐‐2.1 × 10 5 kcal/mol. In the absence of the other two sources of stabilization, each head protein subunit must contribute about 210 kcal/mol of binding energy.