Interaction between bacteriophage T4 coded gene 32 protein and poly(rA)

The cooperative binding of T4 gene 32 protein with polynucleotides, of which the quantitative aspects in the literature have not satisfied the requirements of thermodynamics, is studied by adopting a modified formula of the lattice theory. A moderate value is found for the cooperativity parameter (q approximately 200 at 0.2 M NaCl), which is weakly dependent on salt concentration. The cation effect on the binding suggests that the shielding of negative charges of the protein or a loose cation bridge between the bound protein molecules plays a role in the cooperative binding process.