Hoogsteen base-pairing in DNA replication? Reply

We have solved the crystal structure of human DNA polymerase-? (hPol?) bound to a template primer and incoming nucleotide, and shown that hPol? uses Hoogsteen base-pairing for normal DNA synthesis. Jimin Wang questions the space group we used and claims that Hoogsteen base-pairing is not supported by our electron-density maps. We show here that the issue of space group does not affect our conclusions and that our electron-density maps are clear in indicating that Hoogsteen and not Watson-Crick base-pairing occurs in this situation. © 2005 by Nature Publishing Group.