The editors would like to alert the readers that concerns have been raised regarding some of the data presented in the figures of this article. Specifically:

Fig. 1a AcH3 lanes 3 and 4 appear highly similar;

Fig. 1a H3 lanes 2 and 3 appear highly similar;

Fig. 2a H3 lanes 5–10 and 14–19 appear highly similar (with one lane flipped vertically);

Fig. 2h lanes 11 and 12 appear highly similar;

Fig. 3a (bottom left) the left and right sides of the image appear highly similar (rotated 180 degrees).

Due to the age of the article, the original data are no longer available for validation. Readers are therefore advised to interpret these results with caution.

Alessandro Weisz agrees to this Editorial Expression of Concern. Angela Nebbioso, Emmanuelle Germain, Concetta Ambrosino, Paola Bontempo, Rosana Alvarez, Angel R de Lera, Hinrich Gronemeyer and Lucia Altucci do not agree to this Editorial Expression of Concern. The editors have not been able to obtain current email addresses for Nicole Clarke, Emilie Voltz, Ettore M Schiavone, Francesco Bresciani and Felicetto Ferrara.