Nature Med. 5, 1264–1269 (1999).

On page 1264 in the paragraph beginning "To determine whether...", the second and third sentences were incorrect. The corrected text is printed below.

ED5 cleaved this 23-nucleotide substrate (labeled with 32P at the 5′ end) within 10 minutes (Fig. 1b). The 12-nucleotide product (Fig. 1b) is consistent with the length between the A816–U817 junction and the 5′ (radiolabeled) end of the substrate (Fig. 1a).

We regret this error.