A unique structure of bacteriophage T4 gene 32 protein with double-stranded DNA in low-salt conditions is distinguished by antibodies

Abstract Bacteriophage T4 gene 32 protein (gp32) preferentially binds to single-stranded DNA (ssDNA) to facilitate DNA replication but shows weak binding to double-stranded DNA (dsDNA). Polyclonal and monoclonal antibodies against gp32 were raised, and an enzyme-linked immunosorbent assay was used to evaluate their reactivities against gp32. The reactivity of the monoclonal antibody MGP45 was diminished in the presence of 5 ng/ml dsDNA, suggesting a conformational change that reduces epitope availability. Notably, the same concentration of ssDNA had little effect; instead, 500 ng/ml ssDNA was required to elicit the same degree of inhibition. A decrease in MGP45 reactivity with gp32 was observed in the presence of NaCl at concentrations less than 100 mM under neutral conditions. These changes in antibody reactivity reflect differences the gp32 conformation, which may underlie its different affinities for ssDNA and dsDNA.