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

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 m m under neutral conditions. These changes in antibody reactivity reflect differences in the gp32 conformation, which may underlie its different affinities for ssDNA and dsDNA.