Nat. Struct. Biol. 10, 731–737 (2003).

A mistake was introduced during production of this paper. This mistake was on page 731, line 4 of the second paragraph in the 'Results' section. The correct sentence should read: “The parent (I27)5 homopolymer has been described and is composed of five copies of a mutated C47S C63S domain7,12.” We apologize for any inconvenience this may have caused.