The mechanism of template activation by exonuclease V

In crude extracts from Escherichia coli cells the ATP-dependent exonuclease V was found to be most active in converting double-stranded DNA into a suitable template for DNA polymerase. This phenomenon was studied in some detail with isolated exonuclease V and T7 DNA polymerase. We found that, at ATP concentrations arount 1 mM, the exonuclease produces a broad spectrum of DNA fragments. One class of fragments is largely single stranded with hydrogen-bonded small primer sequences. These structures allow the synthesis of remarkably homogeneous polynucleotide strands by T7 DNA polymerase.