A DNA-binding protein specific for the early replicated region of the chromosome obtained from Escherichia coli membrane fractions.

After extensive dialysis of Escherichia coli membranes treated with Triton X-100, three membrane proteins (A, B and B') with an affinity for DNA have been isolated and purified. They bind to either double-stranded or single-stranded DNA. A and B' proteins preferentially attach to DNA even in the presence of poly(uridylic acid). Only protein B' can recognize some base sequence of DNA because pulse-labelled DNA made at the initiation of replication in a synchronized dnaC mutant has been selectively retained by the protein.