Nature Structural Biology 9, 498–499 (2002).

A mistake occurred during the production of this News and Views report. The observation stated at the bottom of the second column on page 499 was incorrectly referenced to ref. 14. The correct reference for this observation is ref. 12, and the correct sentence is printed as follows: “... the block to splicing due to thio substitution of either Sp oxygen in the domain V loop could not be rescued by Mn2+ (ref. 12).” We apologize for any inconvenience this may have caused.