The major herpes simplex virus DNA-binding protein holds single-stranded DNA in an extended configuration

Properties of the major DNA-binding protein found in herpes simplex virus-infected cells were investigated by using a filter binding assay and electron microscopy. Filter binding indicated that the stoichiometry of binding of the protein with single-stranded DNA is approximately 40 nucleotides per protein molecule at saturation. Strong clustering of the protein in DNA-protein complexes, indicative of cooperative binding, was seen with the electron microscope. Measurements of single-stranded fd DNA molecules saturated with protein and spread for electron microscopy by using both the aqueous and formamide spreading techniques indicated that the DNA is held in an extended configuration with a base spacing of approximately 0.13 nm per base.