Structure of the Escherichia coli DNA polymerase III ε-HOT proofreading complex

The epsilon subunit of Escherichia coli DNA polymerase III possesses 3'-exonucleolytic proofreading activity. Within the Pol III core, epsilon is tightly bound between the alpha subunit ( DNA polymerase) and theta subunit. Here, we present the crystal structure of epsilon in complex with HOT, the bacteriophage P1-encoded homolog of theta, at 2.1 angstrom resolution. The epsilon-HOT interface is defined by two areas of contact: an interaction of the previously unstructured N terminus of HOT with an edge of the epsilon central beta-sheet as well as interactions between HOT and the catalytically important helix alpha 1-loop-helix alpha 2 motif of epsilon. This structure provides insight into how HOT and, by implication, theta may stabilize the epsilon subunit, thus promoting efficient proofreading during chromosomal replication.