The sequence alignments were done with Clustal Omega. Secondary structural assignments on the top are based on the structure determined in this study and colour coded as in Fig. 1a. The residue numbering at the bottom is based on the sequence of MtISWI. The helicase motifs are assigned as reported13. The basic residues involved in AutoN inhibition are highlighted in magenta, and the acidic residues implicated in H4-binding are highlighted in yellow. The residues analysed in this study are indicated with red circles.