The Mechanism of Template Activation by Exonuclease V

Abstract
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 polymerases. This phenomenon was studied in some detail with isolated exonuclease V and T7 DNA polymerase. We found that, at ATP concentrations around 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.