Nature 393, 373–377 (1998); doi:10.1038/30741

It has been brought to our attention that Figs 1a and 5a of this Letter contain some irregularities in the data presentation. Specifically, in the three gel images in the top row and in the rightmost gel image in the second row of Fig. 1a, a black area of the gel was cropped and added to unify the size of the box in order to match the size of the gel images without rescaling. All bands originated from the same gel. The histograms in the right column show quantification of the data from multiple experiments. In Fig. 5a, the similarity between the left and right gel images in the bottom row may be due to accidental duplication. The fact that a long time has passed since publication means it is no longer possible to obtain and investigate the raw data. None of these irregularities affect the original meaning of the experiments, their results, their interpretation, or the conclusions of the paper. Author S.S. is deceased.