Experimental SAD and MAD electron-density maps calculated using one-, two-, three- or four-wavelength data sets. The phases were calculated using SHARP and improved through density modification. The density for the monomer is shown within 1.8 Å from the protein atoms. The clusters and their densities have been removed for the sake of clarity. (a) SAD map calculated with peak data from cycle 1; (b) MAD map derived from peak and low-energy remote data from cycle 1; (c) MAD map derived from peak, inflection-point and high-energy remote data from cycle 2; (d) MAD map derived from peak, inflection-point, high-energy remote and low-energy remote data from cycle 3. The modules are labeled according to the convention in Fig. 1.