Theory of thermal transitions in cohered DNA from phage lambda.

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Abstract
A statistical mechanical theory has been described which is applicable to the analysis of the equilibrium between circular monomer and linear monomer forms of the DNA from bacteriophage [lambda]. The results are in excellent agreement with the hypothesis that the cohesive activity of the ends on this DNA results from base pairing between short, mutually complementary single-stranded regions, high in GC content, and between 16 and 22 nucleotides in total length. Transitions for various sizes and compositions are presented which rule out extensive numbers of AT pairs in the cohered ends. The equivalence of the irreversible and reversible transitions in this case has been demonstrated rigorously. Theoretical curves for the transition between open dimers and linear monomers, or that between cohered half-molecules and free halves, are presented for different concentrations of the DNA. The limiting factor in these calculations is the extent of stacking between the cohered ends and the remaining DNA; this appears to be considerable.