Interaction of a folded chromosome-associated protein with single-stranded DNA-binding protein of Escherichia coli, identified by affinity chromatography

A single-stranded DNA-binding protein (SSB) affinity column was prepared by optimizing the coupling of Escherichia coli single-stranded DNA-binding protein to Affi-Gel 10. The bound SSB retained its ability to specifically bind single-stranded DNA. When nuclease-treated cell extracts were incubated with the SSB beads overnight at 4°C, a major protein of M(r) = 25,000 was bound. At shorter incubation times, two additional proteins of M(r) = 32,000 and 36,000 were also detected. In the absence of nuclease treatment, eight additional proteins ranging from M(r) = 14,000 to 160,000 also bound to the affinity column. The major M(r) = 25,000 protein has been shown to be a folded chromosome-associated protein. Its binding to SSB is strongly enhanced by the addition of DNA polymerase III or DNA polymerase II holoenzyme.