During the past year we measured multiwavelength anomalous diffraction (MAD) from cocrystals of the DNA binding domain of Interferon regulatory factor-1 (IRF-1) complexed to DNA. IRF-1 plays a key role in the regulation of interferons and interferon inducible genes. The MAD data were measured at three wavelengths corresponding to the edge (0.92048?) and peak (0.9198?) of the Br K absorption profile, plus a remote point (0.90496?). Because of the R3 symmetry of the cocrystal, the Freidel pairs could only be recorded by the inverse beam method (f and f + 180o). The data were collected by the oscillation method (Df=1o), with no overlap between successive frames. Inverse data were recorded after every 4-6o of rotation. By the end of the data collection the cocrystal had been rotated 260o. The MAD data were successfully processed and used to determine the structure of this biologically important complex. A manuscript describing the structure is currently in progress. We also measured a high resolution data from crystals of the enzyme FokI in its """"""""free"""""""" state. Crystals of free enzyme diffracted to ~ 3.5? at home, but at CHESS we were able to measure data extending to 2.3? resolution. FokI is an unusual restriction endonuclease that has its DNA recognition and cleavage functions located on distinct subdomains. The structure of the free enzyme will complement the structure of the FokI-DNA complex that was determined using data measured at CHESS during the previous year.
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