In the originally published version of this Letter, there was an error in Extended Data Fig. 7e and the corresponding uncropped blots in the Supplementary Information. The actin bands in the last blot of Extended Data Fig. 7e were duplicates of the corresponding actin bands in the last blot of Extended Data Fig. 7 f. (In the uncropped blot for Extended Data Fig. 7e, the actin bands were mislabelled as 'WDR59' and this led to the error.) Extended Data Fig. 7 and the Supplementary Information of the original Letter have been corrected online. (The Supplementary Information to this Amendment contains the original Extended Data Fig. 7, and the original incorrect Supplementary Information.) We apologise for this error, which does not affect the conclusions of the paper.