Nat. Struct. Mol. Biol. 13, 218–225 (2006); published online 5 February 2006; corrected after print 24 September 2007

The recent paper by Romi et al. (Proc. Natl. Acad. Sci. USA 104, 8791–8796, 2007) was in general agreement with our study of the structure and function of the N-terminal domain of Tetrahymena telomerase reverse transcriptase. However, the two studies disagreed on the effect of a mutation of Trp187 on catalysis, with our study reporting a severe reduction in activity. Upon sequencing the entire gene encoding our W187A mutant, we found that it had a second distant mutation (R812W) in motif C of the reverse transcriptase domain, and we demonstrated that it was the mutation at position 812 that abolished catalytic activity. In addition, we confirmed that authentic W187A telomerase has catalytic activity similar to that of wild-type telomerase. Both studies concur that Trp187 is physically close to the primer-binding site, and in fact Romi et al. have mapped Trp187 as a site of photo-cross-linking to a telomeric DNA primer.

We gratefully acknowledge the work of Arthur J. Zaug (HHMI, University of Colorado-Boulder) in resolving this discrepancy.